When BaseDenom in currency pair is of length 2, such as token OM of Mantra chain, Vote Extensions panic as internally it tries to create DecCoins and it validates denom over OM where it panics.
This leads to error:
ERR recovered from panic in ExtendVoteHandler err="invalid denom: OM" module=server
Line at which this happens
To replicate the issue, try fetching price of OM tokens