The DE is a rather picky gun, in that it only functions very well with the right pressure ammo. There are only a few brands that the factory recommends, one of them being Magtech 240 gr JHP.
A lot of the 44 mag ammo you find has faster burning powder and does not give the right pressure curve this gun needs to cycle that big heavy slide. I have fired mine, a Calif Chrome version,
almost 400 rounds with the only failures due to my right thumb hitting the slide stop during recoil and locking back the action by accident. Limp wristing could also be the problem,
but I am able to fire mine one handed, with my arm being thrown back a ways, and it still cycles fine. since I am a handloader, I reload, using only Accurate #9 powder, which is the powder the factory used to recommend back in the day they when litigation was not a problem. . I did have to send my pistol back a couple weeks after I bought it, , because that stupid Calif firing pin block got jammed.....
I also had them cycle test it with Magtech ammo, and they also said they deburred the bolt too. They were very fast, less than two weeks from day I sent it, and they paid shipping both ways.
So, your friends might need some attention, but I would try some Magtech ammo first, and hold gun tight with both hands, and do not push up on bottom of mag when firing , as that can interfere with
the bolt. Once you get the technique down, the gun is very fun to shoot. I put a 4x pistol scope on mine and last week put 8 rounds into a 2 inch circle at 50 yards.