Are they appearing above the ground while you are within 100m or outside of 100m?

I logged in and spawned in about 3 hours after I logged off, and all 3 of the bags were above ground that I buried near my tent. So within.

Hello.
Please keep us posted in case you come across any other info but it could also be work of a cheater.

Can do l909, but I have doubts that it was a cheater. All the contents were still in all 3 bags.

Are they near a toxic zone / or the edge of the map?

Negative. I have buried the bags again since this happened. So far, they remain buried. Just never had that happen before.

When you make a ticket, you have the option to make it private or public.
If this does happen again, and if the stash spot is special to you, then make a private ticket and report the location and any details you can recall in the ticket.
If there's a bug there, then the more information that the support team has, the better.
As l909 has mentioned, this could be the work of illegitimate players, despite none of the items being removed.

If you do make a private ticket, after you create it, you will need to add a member of the support team as a confidant.

This will probably be on the right side of the page. Add "l909", the moderator in this post, as a confidant.