While playing the adventure Bad Jelly on the test server, I noticed that attacks would not trigger blocks (no attempt was made to roll for a block) against blockable attacks (Small Pseudopod Strike and Able Bludgeon) when facing the enemy. The blocks I had in hand included Block, Parry, Subtle Parry, and Pushback Parry. This occurred both with blocks that I started the battle with as well as those I drew in later rounds. During round four a Hard to Pin triggered, after which my blocks functioned normally. I have not attempted to recreate this bug, but I can if it would be helpful. I did not notice it on any other adventures, though that is not to say it didn't happen.
Oh my god, I never noticed that you couldn't block in mud, that's got to be what it was. Thanks for the response, this topic can be locked.