Mopidy+Rompr - Only few songs are shown when searching for Artist

I am running mopidy with the rompr frontend on a Raspberry Pi Zero. I use the mopidy-local extension to play music from a (self-powered) HDD.
When I use rompr to search for artists, not all the tracks of each album are displayed. This problem only occurs with artists having several albums, also the number of tracks displayed seems to be smaller the more albums an artist has.
When searching directly for an album all tracks are displayed correctly. This problem does not occur when using mopidy-spotify.

Any suggestions to solve this are highly appreciated!

Try Beets + Sqlite backend in and Beets lib backend in Rompr?