Not a big thing but how annoying is it when you jump in to attack a baddie with a ranged weapon and it mistakes you for being inaccessible, so making the hits on the enemy not register, then they casually beat you to death unless you can flee!
I never saw that happen outta reason. Normally the game does that when the pathfinding returns 0, meaning the enemy can't walk to you. So, you probably found a veteran that had an altar, he won't take damage before you destroy the altar. But even those are few and far between, if this is happening to you very often it's gotta be something you are doing.
Ive experienced this several times on my thief using both melee and ranged attacks, its also happened to my gf a few times. While fighting an enemy it will randomly become invulnerable and either keeps attacking or just walks/swims away long enough for its health to regenerate then comes back and fights. I think for me its happened more underwater than on land. Not really a big deal but can be frustrating at times lol.