I also have the same problem in the same environment, but I found a trick to show it again.
- Go to qb icon, right-click, "Show". The qb app bar appears in Ubuntu bar.
- Select Tools and then Settings (or something similar, I'm spanish, :P)
- Maximize Settings window.
- When you double-clicked in Ubuntu menu bar to normlize settings window, it will show you the 2 opened windows.
I also have the same problem in the same environment, but I found a trick to show it again.
- Go to qb icon, right-click, "Show". The qb app bar appears in Ubuntu bar.
- Select Tools and then Settings (or something similar, I'm spanish, :P)
- Maximize Settings window.
- When you double-clicked in Ubuntu menu bar to normlize settings window, it will show you the 2 opened windows.
I hope this will help you!!
Sorry about my english, xD
Regards.