alright, so i've done the following:
a) did chkdsk on card + internal storage
b) re-riped the ones that failed to decode before
c) re-converted the rest of the 3600 files with dbpoweramp flac decoder set to fail on decode failures and to verify files after writing.
d) did the same for the 280 int storage files
e) installed dev build that includes the commit
http://git.rockbox.org/?p=rockbox.git;a=commit;h=fe9a3ceb0e09ae44d15f2636162ea534129b2137 (build starts with fe9a3c)
there are no more broken files afaik
played with the player on the train without card - no issues
inserted the card when home and went for a bike ride and the skipping started almost immediately.
you'd play a few tracks fully, then it plays part of the next and skips to the next track (sometimes near the start, sometimes half way, sometimes near the end). replay the same track - it skips again. fast forward in the track past where it skips, replay track - it doesn't skip anymore - really odd.
the card is a genuine sandisk ultra 128gb (it's had very little use). the player is a 8gb clip+.
about 15mb free on the player, 700 mb on the card.
out of about 50 files I played on the bike ride, at least 5 skipped.
I can't try a new card, I don't own any more especially no more 128gb ones (but given is survived about 256gb read and 128gb write just now i'm very sure there's no problem)
what do we do next? There's nothing really unusual about the flac files as far as i can tell and
here's a copy of rockbox folder/dynamic playlist, etc and ones of the files that displayed the intermittent behavior above. (I'm not sure for this one if the card or the player was playing - suspect card as the other files that skipped are card, but I included both)
https://yadi.sk/d/URRvhd0gqMRcBhttps://yadi.sk/d/g9GGCNcoqMQ6ei'd prefer to remove these in about a week, so please grab copy and let me know what else you might need.