Mirage and Map areas, Un-damagable mobs

Hello, recently I encounter what I think is a bug. Randomly during mapping and enter Mirage mobs would be undamageable. Even if I was able to damage them earlier, whenever I interact with a strongbox or Mirage, all the mobs become invincible. Sometimes it goes away when I portal out and back in, but sometimes it doesn't.

Current, build is Arakaali's fang Necro.

Thank you

Update: seems like it happens mostly when I enter a Mirage
Checked again, definitely joining the Mirage area.