The people that got mobilised late September last year already lead to many reports of extremely poor and lacking equipment, and news like that usually don’t break out of something as gated and hostile to any outside world communications as the Russian army.
Prigozhin and his Wager group got increasingly mad because of that, too, among other things, as they weren’t pumped full of money and best gear the Russian government could muster. They said they were getting g ripped off and such, but what really happened is they got down to the same tier gear as everyone else (maybe higher, still), and that was THAT infuriating to them.