[DiapDealer]

I recommend exempting the Sigil preferences directory (and subdirectories) from any active anti-malware scanning.

%LOCALAPPDATA%\sigil-ebook\sigil\

If you've moved Sigil's preferences folder (via environment variable), and/or temporary work area--especially to a folder that is protected by Windows' Controlled Folder Access security feature--consider reverting to Sigil defaults. The defaults will not use any folders that are protected by Controlled Folder Access (unless you've customized Controlled Folder Access)

I just turn Controlled Folder Access of to be quite frank, but I'm not going to advise others to follow my lead on that.