It could be because of your Armor Class.
In case you are right, then I will just make a Man of steel tank and say f*ck off to all builds who depend on criticals because this would be an ultimate counter measure.Once I convince one of my friends with MoS (unfortunately I myself don't possess any MoS character) to help me with testing, I will conduct some tests to find out who's right.
How do one install a Robot Motivator in the malfunctioned Mr.Handy quest?
It's even worse with Plasma.Finesse basically adds 30% to targets damage resistance.Laser Rifle has Penetrate perk which reduces targets damage resistance to 1/3 of its original value.Plasma Rifle hasn't got that perk so each target gets 30% damage resistance and there are no modificators.
Actually, laser rifle doesn't have penetrate perk and it reduces dt not dr.
Once you have that motivator in your inventory (can be purchased from midget in hub for 800 caps) u click on a robot and dialog box appear. Just choose to repair it with the motivator and it should be ok. 20% repair is enough but you may need several attempts. Also removing stucked piece of junk from the robot seems to help)