Rekordbox doesn't update ratings from memory device nor LINK

I know people have similar issues, but I can't find a right answer.

It used to work before, but now I'm not able to update the rating of a track from a memory device to my collection anymore. Cue points and grid information are updated, but ratings aren't. I use 'update collection' or the 'left-pointing arrow' in Sync Manager (which do practically the same).

Same happens when I try to change the rating via PRO DJ LINK (on a CDJ or XDJ). I can change the star rating on the device, but it's not sending the rating to my collection. It's put back to the old rating on my device when I unpress and re-press the INFO button on my device.

The only way to update ratings is to change in in my collection and then use Sync Manager. But I used to do this on my decks. Why isn't it working anymore?

I'm NOT using iTunes. So all of the answers concerning iTunes aren't valid :-)