We had a problem yesterday.
First Mimic phase was normal. Arcturia went to the middle, mimics came, we killed them, fight went on.
Second or third phase (not sure) went some kind of unexpected.
Arcurira went to the middle, mimics came, we killed them, another mimic, another kill and so on. It won´t stop. After the fifth mimic (playing as a paladin tank i ran out of divinity at this point) arcturia left the middle an attacked us. Mimics won´t stop spawning. So we had Arcturia, mimics and the little guys that spawn, when you don´t manage to kill the mimic in time.
Fortunately our group was strong enough to manage this situation. But I can´t imagine that this is intended.