Don't stress about it uselessly. They most likely got found by a hacker. With esp hack(look it up on youtube) you can see objects and people through the map. It happened to me aswell. Had a bunch of stashes stay where and how i left them for almost a month,then all of a sudden most of them were gone in one day. And i know for a fact it was a hacker as those gone were the ones with the best shit inside them.