Backing up my music, missing files? help

Whilst backing up a pretty large folder of music nearly every sub folder I copy from laptop doesnt have the same amount of files in it when copied to MBL, and there’s so many files that it would be to hard to find which files are missing, any help would be apprecieated , thanks

as you can see, the number of folders is correct but the files are not, in this particular folder there are 6 files missing however in some folders there are 20+ files missing


How are you backing up the files?