Magnetize not pulling in all enemies

[(PS4)sister-hawk 603]

I have begun to notice that Mag’s Magnetize ability is failing to pull in some enemies. The units that I have noticed it the most on are: heavy gunners, bombards, fusion moas, and infested ancients. Though that’s not to say they are the only ones. Sometimes they seem to be able to simply out-pace the pull effect, or they ignore it entirely as if it wasn’t there.