Ive had 2 backpacks just up and disappear. One was transported underground to a area i can't get to(its near a anthill but i checked head to toe and said it wasnt near that area so im certainit isnt just lost). And the second one said it was at the outpost but thats not where I died and it was just a floating icon above nothing. Other than these along with some other bugs I'm sure will be patched up at a later date I quite enjoy the game :3 

go into Game Repair, Recover Backpacks. They should appear outside the Onboarding Facility. If they don't, Save and Load. Even the Issue Tracker says to do that