on server the wallet daemon was working well for ~15 hours but later terminated, at debug.log I see these errors:
2017-08-26 10:27:06 receive version message: /Bitcoin ABC:0.14.6(EB8.0)/: version 70015, blocks=483369, us=78.46.227.52:8333, peer=12454
2017-08-26 10:27:07 ERROR: AcceptBlockHeader: Consensus::ContextualCheckBlockHeader: 000000000000000000639be19a0123a1c99d9fef89f0b8ac055a77f4ef86ae3b, bad-diffbits, incorrect proof of work (code 16)
2017-08-26 10:27:07 Misbehaving: 220.233.129.186:53974 peer=12454 (0 -> 100) BAN THRESHOLD EXCEEDED
2017-08-26 10:27:07 ERROR: invalid header received
2017-08-26 10:27:07 ProcessMessages(headers, 162003 bytes) FAILED peer=12454
2017-08-26 10:27:24 *** System error while flushing: CDB: Error -30973, can't open database wallet.dat
2017-08-26 10:27:24 Error: Error: A fatal internal error occurred, see debug.log for details
2017-08-26 10:27:24 tor: Thread interrupt
2017-08-26 10:27:24 torcontrol thread exit
2017-08-26 10:27:24 scheduler thread interrupt
2017-08-26 10:27:24 addcon thread exit
2017-08-26 10:27:24 opencon thread exit
2017-08-26 10:27:24 Shutdown: In progress...
2017-08-26 10:27:24 net thread exit
2017-08-26 10:27:24 msghand thread exit
2017-08-26 10:27:26 Dumped mempool: 0.070877s to copy, 1.33012s to dump
2017-08-26 10:27:26 *** System error while flushing: CDB: Error -30973, can't open database wallet.dat
2017-08-26 10:27:26 Error: Error: A fatal internal error occurred, see debug.log for details
2017-08-26 10:27:26 CDBEnv::EnvShutdown: Error -30973 shutting down database environment: BDB0087 DB_RUNRECOVERY: Fatal error, run database recovery
2017-08-26 10:27:27 Shutdown: done
Was it the only instance of daemon running (just, if it wasn't, shutdown the other process and it'll fix the problem)?
If you don't have any bitcoin in the addresses in the wallet.dat, you can go ahead and delete it.
If, for educational purposes or you have bitcoin in there, run the net instace of daemon with the -salvagewallet command (this will knock the syncronisation process back to the start).