@sdRohan: Hello! I work for the company that makes DisplayFusion. The issue is definitely that we remove the buttons from the taskbar when the group of windows is moved to another monitor. When we move it back to the primary monitor, we add the buttons back, but understandably, Groupy no longer knows that they should be grouped.
Could we work together to implement a way that we can add the buttons back to the taskbar and notify Groupy that's been done, or something like that? We're open to suggestions 
Even better would be if we could work together to support Groupy groups on the DisplayFusion taskbars as well, so that if a customer moves the group off the Primary monitor, the DisplayFusion taskbar can keep them grouped.
For anyone else that comes across this thread, there are two workarounds:
- Set the Taskbar Mode on the DisplayFusion Settings > Taskbar tab to "Windows taskbar shows all windows, DisplayFusion shows relevant"
- Disable the DisplayFusion multi-monitor taskbar and enable the built-in Windows 10 Multi-Monitor taskbar.
Thanks all!