Device : Emulator : Memu 

OS : Android 7.1

WTR : unknown

Steps : Went to spider den for farming stage 5.

During the middle of the battle, I noticed that the two spiderlings in center left and center right had no meters above their avatars. After watching the battle progress neither spiderling was taking damage or dealing damage. Both spiderlings just sat there idle through the entire battle. 

This issue happened a few times in a row back to back. Trying to grab a screenshot but unsuccessful. 

Hope this helps at least a little.