Playing on xbox one x.  Save files won't load or load incorrectly with all progress lost but backpack inventory intact.  Bombadier beetles don't respawn either.  

well that sucks.  I haven't had a problem yet with my saves (knock on wood or whatever superstition action you want) on the xbox.  you're closing the game out when you finish?  hitting the xbox button, highlighting hte Grounded game, hit the hamburger button (or whatever it's called now) and exit the game.  could be corrupt cache xbox uses to quick load the game and that will clear it.

Sometimes if I load into my friends game I loose all of my inventory and that bothers me.

try to load an autosave before the game loaded with your game reset.  I've been having this issue to but as long as I load an autosave first then it wont overwrite an autosave when it loads with all my stuff gone apart from my inventory.  You can also try re-installing but do this after because it will wipe all your autosaves.  For me autosaves work 100% on xbox but that's only if I'm using autosaves where my game hasn't been reset.