[SOLVED] favorites list stays empty

When I mark items as favourites, I always get the visual feedback, as if adding succeeded, and yet, when I go to the favourites list there are no items in it. /var/log/volumio.log says:

2019-08-11T18:36:36.697Z - info: Adding music-library/NAS/public/lalla/BAP/Bess_demnaehx/2-01 Su 'ne Morje.ogg to favourites using generic method
2019-08-11T18:36:36.716Z - info: Saving local item favourites
2019-08-11T18:36:36.727Z - info: Pushing Favourites {“uri”:"/mnt/NAS/public/lalla/BAP/Bess_demnaehx/2-01 Su 'ne Morje.ogg",“favourite”:false}

I wonder about the third line, ending with “favorite”: false. Does it mean that the item is removed from the favourites again, or does it mean something different?

EDIT: Now it seems to work, for whatever reason. But only for local files, not for podcast episodes, streams. radio stations etc.