The most important thing you need to check into is that your wallet is on the exact same block as our block explorer. If you are mining blocks and those are being rejected it is very likely you are not on the active chain...
Well, I did a fresh install of the wallet.
Checked the blockchain number in the wallet, checked the blockchain number in the explorer. They were the same.
Turned on the debug in the miner, and checked it was running the correct blockchain number, the one in the wallet +1
But I still get: [2018-01-01 18:18:27] accepted: 0/1 (0.00%), 888.54 hash/s (booooo)
[2018-01-01 18:37:17] accepted: 0/1 (0.00%), 981.51 hash/s (booooo)
So I guess something else must be going on!