Ben and I have discovered the root cause for the loss of consensus and have a temporary fix that can be used by all witnesses.
The problem was a single field which we failed to serialize when saving chain state to disk. Any node that didn't replay the chain on startup would have this field reset to 0.
We will be releasing a fix for this along with several other fixes by the end of the week. In the meantime, all full nodes should always replay the blockchain on startup by using the --replay-chain argument.