If you are the person to start a Regional Lair Boss summon and you then try to move a piece of equipment you have equipped to the empowerment window, nothing will happen. Only once the boss pops up will the item then be in the empowerment window. Until then, the item move is queued and cannot be canceled. I only noticed this today because I’m not normally the person who summons our bosses, but I normally try to sneak an empowerment in while people are clicking to summon. I know that this DOES NOT happen if you are simply a clicker. This only happens if you’re the one to use the essence. I assume this will happen on normal Lair bosses as well, but I’ve never really had reason to try to sneak empowerments in during those.
If this can’t be fixed to work as expected then at least don’t queue the item move to happen and give a FIFO popup saying that you can’t unequip items while summoning or something like that. Being left without a weapon when you’re the tank because of this bug can be a big problem.