Pet actions cancelling, delaying, duping and ghosting due to the general AI they have especially when move checks are involved.

The Pet Order commands (Egi Assaults, Enkindles, Devotion) don't resolve when you'd like them to with consistency and still retains bugs from Shadowbringers release.

Bahamut and Phoenix had "summoning sickness" where they couldn't react to GCDs immediately when Bahamut always did in Stormblood. Bahamut was fixed and Phoenix remains in this state.