I created a bunch of virtual copies yesterday and today I opened the same collection and now I have one virtual copy when I created over 100 yesterday. Opened the same catalog by default and RAWs are in the same place on my server. Running LR Classic 10.2 on a Windows 10 Pro machine.
I've tried checking the master and virtual copy buttons at the top right with no help. They aren't stacked and all filters have been reset.
Are they missing from a certain collection, or from the catalog? When you hit the delete key while you are in a collection, the selected images are removed from that collection without any warning or any confirmation dialog. That means this can easily happen by mistake.
"Virtual copies are not created in the folder with the originals but are contained in the catalog"
To clarify your statement-
-Virtual copies are not 'physical' files created on the hard-drive. They only exist as visible previews in the Catalog. (being just another 'text' entry in the catalog database describing a different history of edits.)
-Virtual Copies DO always appear next to their 'Master' preview version in the Library module Folder Grid view, or the 'All Photographs' list.
It is possible to have only the Virtual Copy in a Collection view (without its Master version).