I honestly thought this had already been reported/fixed before, but I looked around and didn't see it posted here. Apologies if this is already known, but, it's kind of a bad bug, losing around 300 hp while you can't do anything. The sound cuts out because I alt-tabbed during the cutscene (I think there should be a way to skip them, or maybe a setting. It does get a bit old watching them over and over, but this is besides the point.), and when I tabbed back in I heard the damage noise and saw my red healthbar. Luckily the clip still captured the Mothball spawning and waddling over to me. I included a bit of the previous room so you can see my previous healthbar so there's no doubt about what happened. This is in Super Frenzy, by the way, if the nest being Imbued matters. I'm not sure if this happens every time or not, I didn't do another run to test it.
Do Super Frenzy Blisterbane Bog, get to the Mothball Nest, maybe watch it spawn an active mothball.
A developer has marked this issue as fixed. This means that the issue has been addressed in the current development build and will likely be in the next update.