I’m not entirely sure if it is the same or relevant but I am (maybe) encountering this bug on some heavy packsize maps.
-Affects all maps with or without immune affix
-Affects monsters which are remnants of an extremely huge, lag inducing mob group
To be clear: That character has Ignore Resist. So I’m pretty sure it isn’t a resists issue… 
-Gybe
I get the untargetable bug maybe once every two maps
I can do single target dps but can’t do damage with my main spell, torrent
For this reason the mob takes 10 minutes to kill (not exageratting) instead of 10 seconds
Looks like the legendary bug - frozen Cartagrapher’s been fixed. Thread unsticked