I have only changed audio quality once, and that’s when I started using KKBOX when I changed the setting to high quality. I’m pretty sure I downloaded songs after changing the setting, not before.
This problem happens depending to album, some albums are safe while others will prompt redownloading.
I first encountered this problem a few months ago. Obviously it was a different version of KKBOX back then.
I do not know if this is related, but in preferences, offline setting is set to “4Gb” which is the maximum possible; I have downloaded 2000+ songs. Is there a limit for downloaded songs?