I have this same issue.
Both server and client are fedora 30. Both run gnome desktop.
Both run turbovnc 2.2.2 from the turbovnc repos.
Restarting the client seems to solve the mouse click hang temporarily.
The easiest way to replicate I found was:
- start firefox remotely
- scroll firefox a lot with mousewheel(two finger touchpad scroll in my case)
- alt tab away from the viewer during the scroll lag
- alt tab back to the viewer
- now the clicks wont work
Regards
/Joakim