I don’t have all the context here but if you have an app in place that has the ability to add/remove products that is generally the best place to start looking.
Your store has an activity log (/admin/activity) so if this happened recently take a look through that. I would guess you’ll see the names of apps removing something. If it was a while ago it might take a lot of clicks to get to that day so be ready for that.
It’s not uncommon for a dropship app to do that if for whatever reason the item is no longer available so your post isn’t raising alarm bells for me quite yet. You mentioned DSers and that’s one app that can delete things.