I will look into this issue (progress can be seen here: https://github.com/kkapsner/CanvasBlocker/issues/161). The faking is working fine on https://browserleaks.com/canvas

EDIT: They are using a very big canvas (400 000 pixels) to do the fingerprinting. It works fine if you disable the "Maximal fake size" ("Maximale Vortäuschgröße") setting. I will adjust the recommendation accordingly.