I wish I could credit the buried reddit post I stumbled on that had the answer for me but I can't find it now..
Anyways, I was just gifted this game from a kind friend and I noticed I could play scav games all damn day with not a single issue, but, soon as I would try to load in my pmc I would pray to get passed the loading loot phase of the connection because it would always black screen out followed by the beautiful prompt telling me it lost connection. The fix? Go to your 'Game' tab in your options, where you would find your pmc's name. Make sure you DON'T have any special characters in your characters name, I had 'Mario' but noticed it counted SIX instead of FIVE characters, there was an entered second line in my name. Probably from a really early iteration of the game where you could cheese your name to look original. Ever since I renamed my pmc from Mario(enter) to OohItzMario I haven't gotten the loot error once and load into my pmc games just like my scav ones now!
I hope this worked for all you guys out there that had this issue that couldn't find a fix as well (I know how many threads I had to search through to find a needle in a haystack)