This just happened to me overnight. Had 256 listings when I went to sleep and woke up to 196 listings. All the missing listings are not in "unsold" or "ended" categories. Used to chat to speak to a rep who had no clue either. No eBay message to say some listings removed, just vanished. eBay wanted the item numbers which I don't keep records of so they could not really help.  Strangely my eBay app still shows the 256 active listings on the home screen but when I click into the 256 it is back down to 196. 

What a mess. I have now gone through and made drafts for all my active listings in case they also disappear. Did anyone whose listings vanish get any explanation from eBay?