Looks like on desktop you can right click on the wishlist item that's missing, and you'll get the URL to the now deleted store page. From there, you can find the Steam app ID of the title (e.g.
https://store.steampowered.com/app/213120/?snr=1_25_4__318
) and then use SteamDB to identify the missing game. In my case, it was
https://steamdb.info/app/213120/
, which is Transformers: Fall of Cybertron.