I think what you have here is incompatibility between an enhanced inventory mod and Valheim's grave inventory (unless you are using one of the "on death" mods, in which case, the two are conflicting. If you have multiple mods which alter inventory slots/systems, you are just asking for trouble. Personally, I recommend the Adventurer's Backpacks mod. You can adjust the various variables, and I have yet to have any "on death" issues (that said, make sure you disable the packs from dropping as loot... that gets annoying).

Disable mod.