Thanks for this fix, @Raymond_Meyer!
I could not get it from right clicking, but I searched and installed the following which worked:
It is very strange - I have recently clean installed Ubuntu 16.04 on my desktop and laptop, and both are using Gnome 3.28.2, but my laptop does not need any fix for the Insync tray icon to display. I have been trying to find a difference between them but have been unable to.
If any dev or user wants me to check something please let me know.