This seems to be logged fairly frequently, but seems to be benign.

 Block synchronization failed — Block has invalid height: Was 135 but expected 136. 

Here, the ledger already advanced when block sync is trying to update it. This might happen because the sync passes the certificates to BFT before trying to advance the ledger. The BFT might then advance the ledger before sync does.
This behavior might also cause #3636.

We should avoid the race condition altogether by ensuring sync only advances the ledger when "syncing" is true, and BFT never advances the ledger when "syncing" is false.