Pretty certain this has been a well known issue for awhile now.
It doesn’t seem to matter what part of the map I’m adventuring in occasionally and sometimes more than occasionally an NPC’s dead body will glitch into the ground rendering it’s body un-loot-able. Heck, I can’t even see the bodies to attempt to loot them. Although occasionally I will get the loot window to pop up.
I also noticed that carcasses in shallow water are not loot-able unless you resource the body with a knife or some other tool first. Then the loot bag will drop.