Xfce4-docklike-plugin - some program icons not loading correctly

I have QubesOS 4.2.4.

Some time ago, I tested the xfce4-docklike-plugin (Panel Plugins / xfce4-docklike-plugin · GitLab) instead of the default taskbar.
I installed xfce4-docklike-plugin via qubes-dom0-update.

I don’t know why some AppVM icons load correctly (e.g., Librewolf, Mousepad, xterm) and some don’t (Thunderbird, xfce4-terminal). I haven’t found any correlation as to why this happens.

I have the problem with all AppVMs. Interestingly, the xfce4-terminal icon from dom0 works correctly, but the xfce4-terminal icon from the “personal” AppVM doesn’t – instead, a blue cube appears (as attached).
Screenshot_2025-08-30_18-04-02

Does anyone know what’s going on?