Observed on ~samzod. It could send messages to ~zod, but not receive messages from it. This occurred in between two syncs.
After turning both ~samzod and ~zod's processes off and on again, ~samzod received messages from ~zod again and continued syncing as if nothing had happened.
I thought there was an issue for this, or a similar case, but couldn't find it when searching.
This may or may not belong in urbit/urbit.