1.4 beta version number: insync_220.127.116.11037-artful_amd64.deb
Operating system: Ubuntu 17.10
I posted here about this issue, affecting insync 1.3, quite a long time ago. Your systray icon is implemented with the discontinued xembed protocol. The reply at the time was that this would be addressed in an upcoming release. Yet, here we are with the same problem in insync 1.4.
xembed support has been dropped from many desktop environments, and replaced with D-bus protocols for interoperability. See, for example:
(and this is several years old!)
The net result is that an icon appears in the systray, but you cannot click on it! Or, at least, clicking on it has no effect. This means trying to configure insync using the insync-headless command, which is poorly documented.