I reported this nearly 5 months ago where it was acknowledged as a bug and its still not been fixed…
Before the outcast engineer patch kruber bot would always heavy attack elites and bosses with his ex sword but now regardless of the type of elite or boss kruber bot will now spam light attacks instead.
To add to this, I often see Kruber using exec heavy attacks vs groups of unarmoured stragglers (fanatics, marauders etc.) with zero armoured enemies in sight merely to eat hits as he finished up his swing.