Works for me in calibre 9.6 on Windows 10.
First thing I'd try is to restore the regex to what it was - not that it should effect the extraction of a cover.
FWIW: I use this regex —
(?P<author>[^_]+) - (?P<title>.+) — I think it's one of the defaults that came with calibre.
How do you do the add - i.e. which one of these
Or some other method, such as
Windows->File explorer->Send to, which is what I use.
BR