I discarded a card during my cleanup because of having 8 cards in hand. The AI had an
Abyssal Nocturnus, which triggered late enough to allow it to keep the +2/+2 bonus until the end of its own turn, meaning it could (and did) attack with it as a 4/4. It should still have been a 2/2, because I didn't discard any cards during the AI's turn.
Cleanup appears to be getting considered as part of the following turn, not a late step in the current turn. This is probably related to the
Thawing Glaciers issue I recently reported (you can safely activate TG during your turn with 7 cards in hand without having to discard one because the triggered bounce, which is supposed to happen during cleanup, doesn't happen until the start of the AI's turn).