i got to the third part of the boss fight and every time i get her down to the mid 40s she disappears and i cant do anything everything just stops spawning and i cant advance

Hi. The forum is pretty inexistent so I don't hold my breath for an answer, but I'm wondering if the Capture All Demon Shield Girls achievement is bugged. I believe I caught each of them, but I didn't get anything though every other achievement of this kind worked. Also, are the slimes just a super rare spawn ? Are they appearing as slimes or as the anime girls ? If anyone can enlighten me, that'll be appreciated. Thanks....