Whenever my Sera is damaged by any source of damage, it's sprite and attacks will stop for 2 secs, and if there are multiple hits on it it can go on semi-permanently, preventing it from leveling.
I have the newest AI and I do not have this problem on any of my other Homunculus. It is level 102 and I disabled all auto-casts in the AI. Is this a Sera exclusive problem or is it just me =(?