Hi @pascal,
Thanks for checking into this.
I have tried everyway I can think of to invoke Popuptoolbar, always with the same result. The primary way I use it is by assigning popuptoolbar with toolbar name to the F4 key and then mapping the F4 button to an extra button on my mouse.
That said I think I found the conflict - I had my command prompt undocked. With the command prompt undocked there are numerous commands that make PopupToolbar stop functioning. The only way that I have found to recover the functionality is to dock the Command Prompt and restart Rhino. With the command prompt docked PopupToolbar functions as expected.
So I guess I won’t undock my command prompt 
Are you able to recreate the same issue with the command prompt undocked?
Having the command prompt undocked in V7 does not cause this issue for me.
Thanks for the awesome support! and congratulations to the McNeel team for another successful release.
Can’t wait to start playing with the Rhino 9 WIP.
Thanks,
John