please read up on how blockchains function.
Maybe you should try just reading the debug.log.
received block
ERROR: CheckProofOfWork() : hash doesn't match nBits
ERROR: CheckBlock() : proof of work failed
ERROR: ProcessBlock() : CheckBlock FAILED
if your seeing this in your log. that means someone found a block on the 'other chain', but is connected to your node..
This is a block from the other chain and your wallet can't proof it because there exsits different PoW algo's. The Problem is that the "switch" realized with a timestamp and not (as usual) with a block number. A if/else in the section in the new version would have solved this issue because is the block before a block number XY use algo 1 and the block mined after a block number XY use algo 2 etc. Now we had the situation that the new version can proof the new blocks BUT if the new version start again and validated the old blocks it use the new algo and not the old (valid for this blocks) algo. correct me if I'm wrong