Update - I genuinely had sneak attack bug out against the owl bear.
I had been always making sure to damage the enemy with Tav first, but after getting a successful sneak attack on the first round, the second round I could not get sneak attack on the frightened, injured owl bear. The only changes were that I had cast bane and the owl bear had moved so it became swarmed by Shadowheart, Tav, and Astarion.
