My first complete import of all folders finally completed last night.
I have 26 Windows folders A,B,C etc for Abba, Billy Brag, Creedance and each has about 14000 files.
F:\music\a
F:\music\b
F:\music\c
etc
F:\coverart\
Tools,options,file location, one folder for music, movies, cover art, do not include cover art in mp3 file
I did import,config auto, select folder A, tick ignore, ok, get cover art, untick rebuild thumbs, tick fix broken links
After import of A folder you should see details icon to see import results.
Scroll down to bottom to see failed imports. Delete these files or move elsewhere.
Next import folder B but remove folder A as it has already been imported.
When you have finished with Z folder go to tools options, tree , thumbnails , rebuild ( may take a long time).
Last week it was MC ver 22.0.59 and now 22.0.77 seems more stable.
Above seems to work for me.