"it seems that another Insync app is currently running.Will quit now"

Ah, looks like this has been covered here:

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I had the same issue for months on Ubuntu 16.04. I’m running version 1.5.5.37367-xenial. What worked for me was:

insync quit
insync start

Seems like an insync bug as tray icons were deprecated. Please make the default .desktop action be show. While making show start insync if not started. Seems like an easy fix.

Part of the reason I use fedora is I won’t have a million icons cluttering my visual space, unlike MacOS

Same problem on ubuntu 16.04