Are you sure they’re being deleted? Federation is a bit weird in that the instance you’re browsing from might not have a piece of content for whatever reason (database rollback/restore or other issues) but if it was posted then it’s out there somewhere on an instance that grabbed it while it was still up.
I also see your account is on “infosec.pub” in the same way mine is on “social.vmdk.ca” so you can try searching on lemmy.world or some other instance for the post in question using keywords. For example I found this on lemmy.world directly while searching for UAP, no idea if it’s what you’re talking about. https://lemmy.world/post/1812373