Here's one which might be a bit tricky to fix, depending on what tools are available. The AI often seems to "forget" things about face-down cards that it has previously seen. The easiest-to-describe example of this is the AI flipping one of the player's monsters facedown (with Book of Moon, Ghostrick Jackfrost, or whatever), then attacking it with a monster that's too weak (and that does not have an effect to justify the attack), resulting in the AI needlessly taking recoil damage. For a human player, mousing over a face-down card that has been previously revealed will show the card info, so clearly the game has some way to flag face-down cards as known, but I have no idea whether the AI has any way to "see" those flags.
And speaking of issues with attack logic and the like, it seems like the AI occasionally has issues with using stat modifiers properly when it's attacking a Defense Position monster (even a face-up one). I can't be sure, but it seems as if, in these situations, the AI is checking the ATK of the player's monster when deciding whether to use its stat modifiers (such as Forbidden Chalice in the Qlis, but there may be other examples), at the point(s) where it should be checking the DEF.