You don't have hard drive in your system? … SSD then? … even SSD can fail
Did you try to just copy those 6 files to some other location? … will at least verify that original files are good (depending on the player, playing them successfully does not always means files integrity is good … like playing damaged CD - might play fine but ripping might reveal damaged tracks)
That is highly unlikely imo … but out of curiosity … is there something special about those 6 files … are they ALAC while rest of files are FLAC? … or maybe are they 24/192 while rest are 16/44.1? … anything that sets them apart from rest of your collection?
Nothing special on these files, encoding, tags, everything.
Tried some tricks to check them, and it seems that the only problem is the playlist.
I've synced them to my android smartphone by JRiver and everything seems fine, including the playlist.
AK70 MKII also has a custom android system on it, so I really don't know what to do now.
Maybe I should just send an email to Astell&Kern.
But those files are not so important anyway, so I've decided not to track this problem anymore.
Thanks for your help!