For sure, the simple answer is to stop quitting via alt-f4. I think if that were the only thing going on though, the game should have resumed back where that .5-3+ second freeze happened a while ago. I should have started again with my inventory from before. Instead, both times, it saved my empty player inventory immediately, but kept the terrain save from previous instances (no grave or marker). This is how (I at least) ended up with a missing corpse.

I told myself to stop F4'ing after it happened the first time and managed to do it again. Fool me once, shame on you, fool me twice, shame on me. It's no doubt my fault I lost my stuff, but it's not as easy as the game going back and restoring my spot from ~20 min earlier. That would have made things much much more tolerable when it had happened to me previously.

The easy fix (to me at least) is that if it really needs to do an insta-save on F4, do it for the corpse too right before you exit. Single player only of course, dedicated servers are unlikely to have these kinds of issues.