Most likely your -datadir parameter is incorrect or it's corrupted which causes bitcoind to download block from beginning.
Please share your debug.log file so we could find the cause.
I think my -datadir is correct, because debit.log sit inside correct directory.
Here is the first 100 rows from my debug.log
-----
$ head -n 100 debug.log.1
2020-04-02T18:19:50Z Bitcoin Core version v0.19.1.0-05f5dd96c (release build)
2020-04-02T18:19:50Z Assuming ancestors of block 00000000000000000005f8920febd3925f8272a6a71237563d78c2edfdd09ddf have valid signatures.
2020-04-02T18:19:50Z Setting nMinimumChainWork=000000000000000000000000000000000000000008ea3cf107ae0dec57f03fe8
2020-04-02T18:19:50Z Using the 'sse4(1way),sse41(4way),avx2(8way)' SHA256 implementation
2020-04-02T18:19:50Z Using RdRand as an additional entropy source
2020-04-02T18:19:50Z Default data directory /home/srg/.bitcoin
2020-04-02T18:19:50Z Using data directory /bitcoin
2020-04-02T18:19:50Z Config file: /bitcoin/bitcoin.conf
2020-04-02T18:19:50Z Using at most 125 automatic connections (1024 file descriptors available)
2020-04-02T18:19:50Z Using 16 MiB out of 32/2 requested for signature cache, able to store 524288 elements
2020-04-02T18:19:50Z Using 16 MiB out of 32/2 requested for script execution cache, able to store 524288 elements
2020-04-02T18:19:50Z Using 0 threads for script verification
2020-04-02T18:19:50Z HTTP: creating work queue of depth 16
2020-04-02T18:19:50Z Config options rpcuser and rpcpassword will soon be deprecated. Locally-run instances may remove rpcuser to use cookie-based auth, or may be replaced with rpcauth. Please see share/rpcauth for rpcauth auth generation.
2020-04-02T18:19:50Z HTTP: starting 4 worker threads
2020-04-02T18:19:50Z Using wallet directory /bitcoin
2020-04-02T18:19:50Z init message: Verifying wallet(s)...
2020-04-02T18:19:50Z Using BerkeleyDB version Berkeley DB 4.8.30: (April 9, 2010)
2020-04-02T18:19:50Z Using wallet /bitcoin
2020-04-02T18:19:50Z scheduler thread start
2020-04-02T18:19:50Z BerkeleyEnvironment::Open: LogDir=/bitcoin/database ErrorFile=/bitcoin/db.log
2020-04-02T18:19:50Z init message: Loading banlist...
2020-04-02T18:19:50Z ERROR: DeserializeFileDB: Failed to open file /bitcoin/banlist.dat
2020-04-02T18:19:50Z Invalid or missing banlist.dat; recreating
2020-04-02T18:19:50Z Cache configuration:
2020-04-02T18:19:50Z * Using 2.0 MiB for block index database
2020-04-02T18:19:50Z * Using 8.0 MiB for chain state database
2020-04-02T18:19:50Z * Using 440.0 MiB for in-memory UTXO set (plus up to 286.1 MiB of unused mempool space)
2020-04-02T18:19:50Z init message: Loading block index...
2020-04-02T18:19:50Z Opening LevelDB in /bitcoin/blocks/index
2020-04-02T18:19:51Z Opened LevelDB successfully
2020-04-02T18:19:51Z Using obfuscation key for /bitcoin/blocks/index: 0000000000000000
2020-04-02T18:20:07Z LoadBlockIndexDB: last block file = 1999
2020-04-02T18:20:07Z LoadBlockIndexDB: last block file info: CBlockFileInfo(blocks=32, size=45428898, heights=621477...621508, time=2020-03-13...2020-03-13)
2020-04-02T18:20:07Z Checking all blk files are present...
2020-04-02T18:20:07Z Opening LevelDB in /bitcoin/chainstate
2020-04-02T18:20:07Z Opened LevelDB successfully
2020-04-02T18:20:07Z Wrote new obfuscate key for /bitcoin/chainstate: b5d8231d442982ad
2020-04-02T18:20:07Z Using obfuscation key for /bitcoin/chainstate: b5d8231d442982ad
2020-04-02T18:20:07Z init message: Rewinding blocks...
2020-04-02T18:20:07Z block index 16927ms
2020-04-02T18:20:07Z init message: Loading wallet...
2020-04-02T18:20:07Z BerkeleyEnvironment::Open: LogDir=/bitcoin/database ErrorFile=/bitcoin/db.log
2020-04-02T18:20:07Z [default wallet] Wallet File Version = 10500
2020-04-02T18:20:07Z [default wallet] Keys: 0 plaintext, 0 encrypted, 0 w/ metadata, 0 total. Unknown wallet records: 0
2020-04-02T18:20:07Z [default wallet] Performing wallet upgrade to 169900
2020-04-02T18:20:11Z [default wallet] keypool added 2000 keys (1000 internal), size=2000 (1000 internal)
2020-04-02T18:20:11Z [default wallet] Wallet completed loading in 3758ms
2020-04-02T18:20:11Z [default wallet] setKeyPool.size() = 2000
2020-04-02T18:20:11Z [default wallet] mapWallet.size() = 0
2020-04-02T18:20:11Z [default wallet] mapAddressBook.size() = 0
2020-04-02T18:20:11Z UpdateTip: new best=000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f height=0 version=0x00000001 log2_work=32.000022 tx=1 date='2009-01-03T18:15:05Z' progress=0.000000 cache=0.0MiB(0txo)
2020-04-02T18:20:11Z block tree size = 621509
2020-04-02T18:20:11Z nBestHeight = 0
2020-04-02T18:20:11Z Bound to [::]:8333
2020-04-02T18:20:11Z Bound to 0.0.0.0:8333
2020-04-02T18:20:11Z init message: Loading P2P addresses...
2020-04-02T18:20:11Z ERROR: DeserializeFileDB: Failed to open file /bitcoin/peers.dat
2020-04-02T18:20:11Z Invalid or missing peers.dat; recreating
2020-04-02T18:20:11Z UpdateTip: new best=00000000839a8e6886ab5951d76f411475428afc90947ee320161bbf18eb6048 height=1 version=0x00000001 log2_work=33.000022 tx=2 date='2009-01-09T02:54:25Z' progress=0.000000 cache=0.0MiB(1txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000006a625f06636b8bb6ac7b960a8d03705d1ace08b1a19da3fdcc99ddbd height=2 version=0x00000001 log2_work=33.584985 tx=3 date='2009-01-09T02:55:44Z' progress=0.000000 cache=0.0MiB(2txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000082b5015589a3fdf2d4baff403e6f0be035a5d9742c1cae6295464449 height=3 version=0x00000001 log2_work=34.000022 tx=4 date='2009-01-09T03:02:53Z' progress=0.000000 cache=0.0MiB(3txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000004ebadb55ee9096c9a2f8880e09da59c0d68b1c228da88e48844a1485 height=4 version=0x00000001 log2_work=34.32195 tx=5 date='2009-01-09T03:16:28Z' progress=0.000000 cache=0.0MiB(4txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000009b7262315dbf071787ad3656097b892abffd1f95a1a022f896f533fc height=5 version=0x00000001 log2_work=34.584985 tx=6 date='2009-01-09T03:23:48Z' progress=0.000000 cache=0.0MiB(5txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000003031a0e73735690c5a1ff2a4be82553b2a12b776fbd3a215dc8f778d height=6 version=0x00000001 log2_work=34.807377 tx=7 date='2009-01-09T03:29:49Z' progress=0.000000 cache=0.0MiB(6txo)
2020-04-02T18:20:11Z upnp thread start
2020-04-02T18:20:11Z UpdateTip: new best=0000000071966c2b1d065fd446b1e485b2c9d9594acd2007ccbd5441cfc89444 height=7 version=0x00000001 log2_work=35.000022 tx=8 date='2009-01-09T03:39:29Z' progress=0.000000 cache=0.0MiB(7txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000408c48f847aa786c2268fc3e6ec2af68e8468a34a28c61b7f1de0dc6 height=8 version=0x00000001 log2_work=35.169947 tx=9 date='2009-01-09T03:45:43Z' progress=0.000000 cache=0.0MiB(8txo)
2020-04-02T18:20:11Z torcontrol thread start
2020-04-02T18:20:11Z UpdateTip: new best=000000008d9dc510f23c2657fc4f67bea30078cc05a90eb89e84cc475c080805 height=9 version=0x00000001 log2_work=35.32195 tx=10 date='2009-01-09T03:54:39Z' progress=0.000000 cache=0.0MiB(9txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000002c05cc2e78923c34df87fd108b22221ac6076c18f3ade378a4d915e9 height=10 version=0x00000001 log2_work=35.459454 tx=11 date='2009-01-09T04:05:52Z' progress=0.000000 cache=0.0MiB(10txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000097be56d606cdd9c54b04d4747e957d3608abe69198c661f2add73073 height=11 version=0x00000001 log2_work=35.584985 tx=12 date='2009-01-09T04:12:40Z' progress=0.000000 cache=0.0MiB(11txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000027c2488e2510d1acf4369787784fa20ee084c258b58d9fbd43802b5e height=12 version=0x00000001 log2_work=35.700462 tx=13 date='2009-01-09T04:21:28Z' progress=0.000000 cache=0.0MiB(12txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000005c51de2031a895adc145ee2242e919a01c6d61fb222a54a54b4d3089 height=13 version=0x00000001 log2_work=35.807377 tx=14 date='2009-01-09T04:23:40Z' progress=0.000000 cache=0.0MiB(13txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000080f17a0c5a67f663a9bc9969eb37e81666d9321125f0e293656f8a37 height=14 version=0x00000001 log2_work=35.906913 tx=15 date='2009-01-09T04:33:09Z' progress=0.000000 cache=0.0MiB(14txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000b3322c8c3ef7d2cf6da009a776e6a99ee65ec5a32f3f345712238473 height=15 version=0x00000001 log2_work=36.000022 tx=16 date='2009-01-10T04:45:46Z' progress=0.000000 cache=0.0MiB(15txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000174a25bb399b009cc8deff1c4b3ea84df7e93affaaf60dc3416cc4f5 height=16 version=0x00000001 log2_work=36.087485 tx=17 date='2009-01-10T04:45:58Z' progress=0.000000 cache=0.0MiB(16txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000003ff1d0d70147acfbef5d6a87460ff5bcfce807c2d5b6f0a66bfdf809 height=17 version=0x00000001 log2_work=36.169947 tx=18 date='2009-01-10T05:03:11Z' progress=0.000000 cache=0.0MiB(17txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000008693e98cf893e4c85a446b410bb4dfa129bd1be582c09ed3f0261116 height=18 version=0x00000001 log2_work=36.24795 tx=19 date='2009-01-10T05:12:14Z' progress=0.000000 cache=0.0MiB(18txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000841cb802ca97cf20fb9470480cae9e5daa5d06b4a18ae2d5dd7f186f height=19 version=0x00000001 log2_work=36.32195 tx=20 date='2009-01-10T05:22:54Z' progress=0.000000 cache=0.0MiB(19txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000067a97a2a37b8f190a17f0221e9c3f4fa824ddffdc2e205eae834c8d7 height=20 version=0x00000001 log2_work=36.392339 tx=21 date='2009-01-10T05:39:55Z' progress=0.000000 cache=0.0MiB(20txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000006f016342d1275be946166cff975c8b27542de70a7113ac6d1ef3294f height=21 version=0x00000001 log2_work=36.459454 tx=22 date='2009-01-10T05:49:13Z' progress=0.000000 cache=0.0MiB(21txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000098b58d427a10c860335a21c1a9a7639e96c3d6f1a03d8c8c885b5e3b height=22 version=0x00000001 log2_work=36.523584 tx=23 date='2009-01-10T06:04:27Z' progress=0.000000 cache=0.0MiB(22txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000000cd339982e556dfffa9de94744a4135c53eeef15b7bcc9bdeb9c2182 height=23 version=0x00000001 log2_work=36.584985 tx=24 date='2009-01-10T06:06:51Z' progress=0.000000 cache=0.0MiB(23txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000fc051fbbce89a487e811a5d4319d209785ea4f4b27fc83770d1e415f height=24 version=0x00000001 log2_work=36.643878 tx=25 date='2009-01-10T06:17:57Z' progress=0.000000 cache=0.0MiB(24txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000008e35a1d59ea1be8d76683662f47fd13c62a9e347ad5845a26f762026 height=25 version=0x00000001 log2_work=36.700462 tx=26 date='2009-01-10T06:24:06Z' progress=0.000000 cache=0.0MiB(25txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000041438e52d25bccab8798a92cabafdaad69a071d3d2a41718faf01098 height=26 version=0x00000001 log2_work=36.75491 tx=27 date='2009-01-10T06:54:10Z' progress=0.000000 cache=0.0MiB(26txo)
2020-04-02T18:20:11Z UpdateTip: new best=0000000071350772f98f84babf35502b33d42ee8466d3dde0f376c4120352081 height=27 version=0x00000001 log2_work=36.807377 tx=28 date='2009-01-10T06:56:13Z' progress=0.000000 cache=0.0MiB(27txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000bb0d9430d3d1bab474be5050342161efcca9f7e45b151bff9a700944 height=28 version=0x00000001 log2_work=36.858003 tx=29 date='2009-01-10T15:30:57Z' progress=0.000000 cache=0.0MiB(28txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000c57a1b6351208c592eef8eff015d93c899a047fe35b35252a4a59bcb height=29 version=0x00000001 log2_work=36.906913 tx=30 date='2009-01-10T15:31:43Z' progress=0.000000 cache=0.0MiB(29txo)
2020-04-02T18:20:11Z init message: Starting network threads...
2020-04-02T18:20:11Z UpdateTip: new best=00000000bc919cfb64f62de736d55cf79e3d535b474ace256b4fbb56073f64db height=30 version=0x00000001 log2_work=36.954218 tx=31 date='2009-01-10T15:42:02Z' progress=0.000000 cache=0.0MiB(30txo)
2020-04-02T18:20:11Z UpdateTip: new best=000000009700ff3494f215c412cd8c0ceabf1deb0df03ce39bcfc223b769d3c4 height=31 version=0x00000001 log2_work=37.000022 tx=32 date='2009-01-10T15:52:16Z' progress=0.000000 cache=0.0MiB(31txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000e5cb7c6c273547b0c9421b01e23310ed83f934b96270f35a4d66f6e3 height=32 version=0x00000001 log2_work=37.044416 tx=33 date='2009-01-10T15:59:31Z' progress=0.000000 cache=0.0MiB(32txo)
2020-04-02T18:20:11Z UpdateTip: new best=00000000a87073ea3d7af299e02a434598b9c92094afa552e0711afcc0857962 height=33 version=0x00000001 log2_work=37.087485 tx=34 date='2009-01-10T16:12:19Z' progress=0.000000 cache=0.0MiB(33txo)