randomly while playing the my character dies about 15 minutes into the game, has happened multiple times, may have something to do with opening my inventory as last time it occurred i had just stopped to check my inventory

last time it happened my character wasn't sick, injured or cut. my health, thirst, hunger and temperature were all good. there were no negative indicators on my HUD
i wasn't wet or cold. i was hiding in a shed, the door was closed. there were no zombies in the shed or outside. i had not seen any players around before entering the shed and i looked around the shed and there were no players inside.

i saw a 3 dial lock on the ground which i wanted and i opened my inventory while my character was facing the shed door so i could move stuff round to make room for the lock. while moving my stuff around my character died instantly. as i could see through my inventory i know the door hadn't opened. there were no windows in the shed i was in. so no way for someone to have killed me. there was no gun shot, or zombie screams, no sounds to indicate that there was an enemy around to kill me.

i don't know if i'm just missing something but the circumstances of the incident seems impossible and it appears to have happened a few times always after about the same amount of game time