Same problem here with Ristretto 0.8.2. When there are some thumbnails for a folder (i.e. generated by Thunar) then Ristretto will display them. But Ristretto 0.8.2 will not start generation of thumbnails.
With Ristretto 0.8.0 this worked well.
Same problem here with Ristretto 0.8.2.
When there are some thumbnails for a folder (i.e. generated by Thunar) then Ristretto will display them. But Ristretto 0.8.2 will not start generation of thumbnails.
With Ristretto 0.8.0 this worked well.