On the level 62 monolith " The Stolen Lance" the Argentum Spire the enemies were immortal. It happened when the boss spawned the ads. I also have the unique ring Arboreal Circuit Ring which spawns Illusory Tree not sure if that is effecting the enemy minions too.
I also beat this monolith once already with this same exact build before the recent patch. I noticed the health bars not going down when I was attacking and I thought maybe they had tons of health or something. I was trying to kill the ads for about 5 minutes untill I exited to the login screen.
Update
I tried again after exiting from the login screen and I was able to finish it this time with no immortal ads. I don’t know what is going on with this game in terms of things breaking in the moment and then restarting the game fixes it temporarily.