We have a liveness regression on genki-3000 a community testnet for Cosmos SDK v0.28.

What happened was the proposer proposed an invalid block because they were running SDK v0.28-rc2, the network completed the prevote round and then voted nil in the precommit. Polka on nil for the prevote round happened.

Then then everyone got stuck and the next round didn't start.

Restarting validator and sentry nodes causes the votes to progress to the next round.