I have DisplayFusion taskbar enabled for all my monitors, except for my primary one. For some reason, this app that I use called Parsec will only show the taskbar icon on my primary monitor (i.e just with the default Windows taskbar). Even if I move the Parsec window to the other monitors, the taskbar icon will not follow.
If I disable DisplayFusion taskbar, then the icon will follow just fine. It is only when I move to a monitor that has the DisplayFusion taskbar that the icon will not follow.