It's not a bug, it's a feature 😉
The opponents Dr Blight causes affliction on your Wave Brood. (see the little green skull over it?). That means the monster can not be healed.
When it was resurrected it came back without it (see it disappear when it comes back on stage?). So now it can be healed by triage.
Oh I see now. I didnt catch that before. I watched that over and over to lol. Thanks for the info.