I have had an issue for a long time where InSync does not terminate when quitting. The GUI closes, but the backgound Insync and Insync finder integration process never stop.
Hi! This is Mara from Insync Support. 
How do you close the app? Do you click on the Quit button to close it?
@Stuartbr Hi! Could you send your logs.db and out.txt (guide here) so we can check why the process doesn’t quit completely?
Please email them to support@insynchq.com with the link to this post. Thanks!