Clear Cache doesn't seem to be working?

My Windows PC is set on auto-optimize. I have an external drive connected to it, set to be a vault (as well as Google Drive).

I chose Clear Cache on the laptop. It found lots (~4000) of previews and thumbnails to remove. (If I’m understanding correctly, I suppose this may be related… I’ve been doing various import tests and at first the PC hard drive was a vault but now it is auto-optimize.)

I accepted the default, to remove them all. It showed a dialog box (“emptying Mylio cache”) while it was removing them. The dialog box showed that all ~4000 were removed, and closed.

A few minutes later, I tried Clear Cache again. It found another several 1000 to remove. Doesn’t this imply that the first Clear Cache attempt failed? I really wasn’t expecting that.