That bug happened several times to me.
Just now when fighting the wurm with my engineer with the flame thrower flame jet always stopped attacking after one attack even though it is set to auto attack and I was standing right next to the worm.
Just writing about this now reminds me of another bug that might be related to that. Trying to attack the Golem MKII with a FGS often causes an “obstructed” message. Even though there is nothing in the way and I am close enough. And my earth elemental runs to the Golem or the Wurm punches it once and then runs back to me and then back to the boss, rinse and repeat….
So could it be that the auto attack doesn’t continue to attack because somehow the game things the enemy is obstructed?
But then I also could not resurrect someone. Pressing “F” did nothing.
I definitely had the wurm as a target and I was not writing accidentally in chat.