The CloudMirror doesn't generate thumbnails using the ThumbnailProvider.

The Initialize method correctly gets called for each path, but the GetThumbnail doesn't seem to ever get called. Ultimately, the thumbnail does not load to the client.

I looked at #2, but that seems to be about the more general shell registration. The shell registration and registered handlers (or at least the custom command, I haven't tried the others) do work, including the call to ThumbnailProvider.Initialize.

C++ version

Running the latest from Windows-classic-samples gets thumbnails in the file explorer. (Oddly, breakpoints in GetThumbnail are not hit, and wprintf added to it does not show up in the console. I don't know whether that means it's actually getting the thumbnail in some other way, or that it's some threading change that runs the GetThumbnail method in some other context outside the debugger/console.)