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This is what I got after upgrading Confluence to a version above 6 (6.3.3 in my case), this is an issue caused by a too old version of httpd/apache as a reverse proxy and since we don't need the collaborative editing function we needed to find out how to disable it to get our system going again.
I know there is a python script for the rest API and you can use to web GUI and so on, but if you tried those you prabably already found out you can't kill the damn Synchrony process or get it disabled no matter how hard you try...
The easy solution is to go to Manage add-ons -> Select the view for the system add-ons -> And disable these 2:
Synchrony Interop Bootstrap Plugin
Confluence Collaborative Editor Plugin
And restart confluence to make sure it is permanent.