Have you changed mags by any chance from one day to the other? KWAs are notoriously picky about what will feed in them. My KWA just barely poops out bbs if I try and use anythin but VFC, MAG, and KA mags.
Also if you are slamming your mags in to make sure they're seated, you may have created a little space between the hopup and the mag and you'll lose compression that way.