¿How does it happen? I mean, ¿You get a good chunk of their health and they suddenly regenerate? I'm actually pretty curious about it, it's never happened to me before...
Post a thread on the Issues and Bugs forum, here's the link: https://forum.skullgirlsmobile.com/forums/known-issues-bugs.27/
Be more specific about it though, if you have video or photo evidence, share it there, along with as much details as possible (You and your enemy's team, his name, game mode you were playing on, recreate the scenario, etc.)
That sounds like a G.I.Jazz Big Band or some fight modifier. Remember to check the pause menu to see exactly what might affect your battle! Hex, buff removal, heal block, bleed and armor break all help deal with G.I.Jazz too.