It makes sense when you realize they're using off-the-shelf walkie talkies instead of encrypted radio in many areas and other older, less useful equipment everywhere. The funding for upgrading and maintaining their forces was diverted to the oligarchy, and they're making do with whatever they can find. The drones made with off-the-shelf components are a good example as well. I mean, does it make sense for the Russian military to all be using open radio bands to discuss battle plans when the Ukrainians can listen in?!?!? Heck no. Of course they have encrypted radio - but not enough, and the ones they have are of different, incompatible types. So for the units of one type in one area to talk to units of a different type that's incoming, they use the open air radio b/c it's the only thing they can do to communicate. Better equipment exists, but they don't have it. Same is likely with this GPS. It was cheap and it worked, so they used it.
Troops are leaving behind expired rations, expired med kits, paper maps from the 90s, and other archaic things. We're not talking expired by a few months, either - expired by decades. Much of the heavy equipment is decades old - some dating back to WWII.
But, their biggest problem is that their supply lines are heavily debilitated. That coupled with the fact that their equipment was designed for nuclear warfare tactics and their generals have no experience with this type of warfare is crippling. They first thought Ukraine would fold under intimidation, then thought the fight would be similar to Syria. It's just been mistake after mistake & they're now lobbing cluster bombs and lots of older, terribly imprecise missiles at the region.
Ukraine has pushed Russia back to the disputed areas, but the war will go on until Russia has had enough. The borderlands are much easier for Russia to resupply and control what land they hold. Barring a nuclear launch, I don't see Russia taking an inch of Ukraine, and quite possibly losing Crimea as well. The Ukrainians are in no mood to negotiate after what Russia has done to their people.