Sure not everything is running as expected, because the block chain includes some more modifications as with a normal release 
And of course Not sure what's wrong. My nodes are all running without issues.
In the sources:
// Check proof of work
if (nBits != GetNextWorkRequired(pindexPrev, this))
return DoS(100, error("AcceptBlock() : incorrect proof of work"));
GetNextWorkRequired() uses the methods GetTargetSpacing() and GetInterval() to calculate the next difficulty. Maybe the issue is that those methods depends on GetNetworkHashPS()? But I think GetNetworkHashPS() should always return the same hashrate.
And of course Not sure what's wrong. My nodes are all running without issues.In the sources:
// Check proof of work
if (nBits != GetNextWorkRequired(pindexPrev, this))
return DoS(100, error("AcceptBlock() : incorrect proof of work"));
GetNextWorkRequired() uses the methods GetTargetSpacing() and GetInterval() to calculate the next difficulty. Maybe the issue is that those methods depends on GetNetworkHashPS()? But I think GetNetworkHashPS() should always return the same hashrate.