It's hard to see in the picture, but while playing with Grant in the Entrance Corridor (Castlevania Adventure) I started to take damage even when no enemy was hitting me. It happened after summoning and fighting the giant bat. I think something happened with that boss, after he turned into a bunch of bats it never came back to its original form and I couldn't defeat it (couldn't get the unlock for Christopher). If I stood still, Grant would take a lot of damage, so I started moving. When moving, I took less random damage, but I was still losing hp even with no visible enemies hitting me. That made me think like an invisible and invulnerable enemy was following and damaging me. Maybe the giant bat turned invisible and invulnerable after it didn't turn into its original form (after defeating the group of bats). After losing the stage, I played it again and rushed the boss and defeated it after it turned into a group of bats several times. Maybe damaging the giant bat too fast triggers the bug, I don't really know if the random damage is related to the giant bat, but that is the only thing I can think of.
Operating System: Windows 10
Platform: Steam
Game Version: v1.14.105 (49316561R)