Why some icons look weird in Qubes?

Maestral is simply blank.
Mattermost and Owncloud only show dot at the corner of the icon, not the icon itself

I’ll add that the provided Firefox icon is so low-res that if it’s any larger than the one on the toolbar it’s just a big fuzzy blob. Add in the color shifting and it’s unrecognizable.

Hm, launcher icons look fine to me. But tray icons do not.