Wisp Empowered Rare Bug?

Me and a few friends had to fight a wisp empowered rare in Act 3 Jungle Ruins non cruel a lvl 30-31 area. That respawned 9 times. Not sure if this is a bug but wanted to make sure that it is brought to your attention. Every time we killed it, it respawned and gained a new wisp modifier eventually becoming unkillable for a lvl 30 character that would be in that zone. Once it reached 9 modifiers it finally died

All in All it took us about an hour o finally bring down. It dropped 4 Unique Gloves and a metric crap ton of rare and magic gloves each time it was killed.

I ran into this problem solo at level 92. It kept coming back with so much power that after 6 kills, I eventually died to a mathematically unkillable foe. Which closed out my waystone. I have more waystones, but that mechanic is garbage. Ton of stuff on the ground but havent a clue what it was. With only 1 fighter, there was never any time to look during the 15 minutes of straight fighting.

It isn't the worst problem in gaming. But its a neat mechanic that gets ruined with a sh*t outcome for high end solo players.