So the problem is as follows:
I downloaded a certain number of Djvu books. When I open the location in Thunar, no thumbnail is shown. "Show thumbnails" option in Desktop Settings is enabled. PDF files are previewed correctly, and in /usr/share/evince-thumbnailer/ image/vnd.djvuexists as an option. I tried adding additional types of djvu mime codes to the thumbnailer desktop file but no work! Tried to manually run evince-thumbnailer $i $o on a file gave the correct output. I also tried to get the available ARCH extension which is alike the mentioned evice-thumbnailer command (almost exact).
If you need any additional information, I would like to solve this since on all 4 machines I use Xfce.