Artist Images don't show

In the artist tab, all the images of the artists have disappeared an been replaced by the placeholder image. Now at first all of them were removed and I thought that there was a problem with the version that I used, so I updated volumio. Now when adding new music, the artist image shows, but not with the artists that were already there (see image: bill evans trio, bohren en buena vista are new; bb king, beck and cat power were already there). Does anybody know haw to fix this?

Volumio Information

Volumio Version:2.806
Hardware: Raspberry Pi 4 (4gb)
DAC: Hifiberry Dac Pro+