QSystemTrayIcon no icon Wayland/StatusNotifierItem on Labwc(compositor)

QSystemTrayIcon doesn't display icons when using Wayland and a tray implementing StatusNotifierItem.

Message being shown:

QSystemTrayIcon::setVisible: No Icon set.

What is weird is that some icons are being shown. I have verified that the icon theme contains the requested icons. Here's an excerpt from the dbus log:

Working icon:

      dict entry(
         string "IconName"
         variant             string "video-display"
      )

Not working icon:

dict entry(
         string "IconName"
         variant             string ""
      )

The string is empty for some reason. Why isn't it getting the proper icon passed?

I am experiencing this with a Python program and using PyQt6. The Wayland compositor I'm using is Labwc and the tray is implemented by Waybar, but I have tested it with other trays implementing the SNI protocol and they have the same issue.

I have attached a test program and the complete dbus message log of a working icon and a missing icon. The icon theme which I tested it with is the Adwaita icon theme. The icon which works is "video-display". An icon which doesn't work for example would be "audio-volume-high".