I have had this happen too

Are you going back to the same barrel on the same server when this issue occurs?

You have to hold x and have the appropriate inventory space

I’ve had this happen in a variety of things. Tents, fire barrels, enemy clothing when looting their corpses. Normally there is a way around the bug, but sometimes you still can’t get items. If you leave the server and come back sometimes that works. Sometimes you have to scroll in from the bottom of the inventory screen or the top. Sometimes you have to pick up what your trying to loot(bag or clothes) to get the items stored inside.

And sometimes it won’t let you pick up items because some one else picked it up previously and for some reason the item is still visible to others but can’t be picked up.

Please add detailed happenings to reproduce glitch. The more in depth explanation the more likely it will be addressed