Don't know why, only know it happened me 8 times and only 1 block was credited to my wallet.
After more analysis, it turns out that, out of these 8 times a new block was found, "ERROR: AcceptBlock()" was triggered 6 times, while in the other instances I got:
CheckWork() : new proof-of-work block found
proof hash: 00000000486a2ca96a044c9bbe628c1a334356ef49f7ad3af63890558a9fa1d0
target: 000000005818c600000000000000000000000000000000000000000000000000
CBlock(hash=0af4830d9ce404d5b7fe163c7afc8314b96abc2915766bea222a59db5199c55b, ver=7, hashPrevBlock=f34845a0dafa1161726930992e0d0a20c8a530ecad401c4984ddb32c62315d28, hashMerkleRoot=0808bdd904183c6cf810f7cfd3f8$
Coinbase(hash=0808bdd904183c6cf810f7cfd3f8dddd7796387f220383859a7affe0f91d0503, nTime=1504310401, ver=1, vin.size=1, vout.size=1, nLockTime=0)
CTxIn(COutPoint(0000000000, 4294967295), coinbase 028e2b0101)
CTxOut(nValue=4.00, scriptPubKey=OP_DUP OP_HASH160 a37e0d6ccc7e3ed254d1d990f8f8d6af7053d710 OP_EQUALVERIFY OP_CHECKSIG)
vMerkleTree: 0808bdd904183c6cf810f7cfd3f8dddd7796387f220383859a7affe0f91d0503
generated 4.00
keypool keep 7
AddToWallet 0808bdd904183c6cf810f7cfd3f8dddd7796387f220383859a7affe0f91d0503 new
SetBestChain: new best=0af4830d9ce404d5b7fe163c7afc8314b96abc2915766bea222a59db5199c55b height=11150 trust=145514044351268806619 blocktrust=12480725596 date=09/02/17 00:00:16
ProcessBlock: ACCEPTED
keypool added key 108, size=101
keypool reserve 8
REORGANIZE
REORGANIZE: Disconnect 1 blocks; f34845a0dafa1161726930992e0d0a20c8a530ecad401c4984ddb32c62315d28..0af4830d9ce404d5b7fe163c7afc8314b96abc2915766bea222a59db5199c55b
REORGANIZE: Connect 1 blocks; f34845a0dafa1161726930992e0d0a20c8a530ecad401c4984ddb32c62315d28..de2429afaae3b1dc991ad4112e06335ef6364dfd2dca6e677430c30930544195
REORGANIZE: done
which was NOT credited, and
CheckWork() : new proof-of-work block found
proof hash: 0000000046b9fa8caf298642389086beaef341b9ca4f79cba8b5493894d530cf
target: 0000000097f40000000000000000000000000000000000000000000000000000
CBlock(hash=086fd38cc5d43d1bb2be800cfa402476498b4e41a9c0e2c68f9f53f8ee0ed2d3, ver=7, hashPrevBlock=03c268ecd778c622d4a631ae76e59e626825e0ded1024b8bef8c963bc40642ae, hashMerkleRoot=5036ff09695329beebff3d608e73$
Coinbase(hash=5036ff09695329beebff3d608e73ae96abf7d69cc1176b7320a4cb48ff039a11, nTime=1504333570, ver=1, vin.size=1, vout.size=1, nLockTime=0)
CTxIn(COutPoint(0000000000, 4294967295), coinbase 02212e0101)
CTxOut(nValue=4.00, scriptPubKey=OP_DUP OP_HASH160 3e742215294dc924c7c85575d291f6b66e617b1a OP_EQUALVERIFY OP_CHECKSIG)
vMerkleTree: 5036ff09695329beebff3d608e73ae96abf7d69cc1176b7320a4cb48ff039a11
generated 4.00
keypool keep 9
AddToWallet 5036ff09695329beebff3d608e73ae96abf7d69cc1176b7320a4cb48ff039a11 new
SetBestChain: new best=086fd38cc5d43d1bb2be800cfa402476498b4e41a9c0e2c68f9f53f8ee0ed2d3 height=11809 trust=158765568409155339721 blocktrust=7235860583 date=09/02/17 06:26:16
ProcessBlock: ACCEPTED
keypool added key 110, size=101
keypool reserve 10
which was instead credited.