I recently upgraded to Windows 10 from Windows 7, and it has come with its share of issues.
MC 26 worked flawlessly in 7, unfortunately not so well in Windows 10, so I really can't fault the program as much as the new OS.
Some of my music files, the ones that were either iTunes (before I upgraded to MC) or CD Rips to FLAC would appear in the library after importing, but wouldn't play due to read errors.
I was able to surmount that issue by painstakingly changing file permissions for all the songs in each folder. Then the songs would play.
The only problem now is that , even using drop and drag, auto import, or individual folder import, some folders will simply not import to the library. If I go to the folder, I can play individual tracks. So playing the music isn't the issue as much as getting the files to import.
If anyone has had similar issues importing, I would appreciate any advice.