Rating is not synchronised from XMP files

I’m using 3rd party app for photo culling. The app creates XMP file with a star rating, which is loaded by PhotoLab (5.1.1 build 52). It mostly works, but when there is a lot of photos (currently 700+), the rating is not loaded.
I tried different folder with a few photos (without restarting any application) and synchronisation works. However, these folders does not need filtering :slight_smile:

Is it a bug or am I doing something wrong?