Hi, sorry to hear that! An upgrade absolutely should not remove your stash, but to figure out the cause, I'll need some more info from you about what happened/what exactly you saw. Can you please open a bug report here: https://github.com/josh-berry/tab-stash/issues/new/choose

In the meantime, there is one known issue which sounds similar--if it's the same issue, your stashes aren't actually lost, they're just not shown in the UI. This can happen if you have another folder or bookmark with the exact name "Tab Stash" anywhere in your bookmarks tree. Here is the issue, I've added some steps to investigate and a workaround in the comments: https://github.com/josh-berry/tab-stash/issues/41