I've just opened Sigil to edit the margins in a book as they are a little too small. When I did all my preferences, saved searches, plugins, saved clips, etc were missing. Sigil's GUI had reverted to its default state.
I installed V1.8.0 on 25 October 21 and I have edited books since then and there were no issues with Sigil. I'm running Windows 10 Home on a Dell Inspiron laptop.
I've attached a screen shot showing the current .INI files from my laptop on the left hand side of the image. The right hand side shows the files from a backup last week.
The only thing I've been doing that I haven't used regularly before is using Calibre's 'Send to device' option to load my library onto my new ereader.