320kbps should be fine. You might try wiping out the tunes and then re-transferring them to your player. Or, if that doesn’t work, open the problematic tunes in freeware MP3Tag ( an ID3 tag editor) and see if you see any issue, such as extra-long tags (including in the Comments field).
Also, the tags should be set to ID3v2.3 ISO-8859-1 format. If not, simply set that format within MP3Tag, select/highlight all the files, and then resave.