I fixed the SID problem for the majority of cases. The main problem were wrong domains. The configured cookie-domain was wiki.ardupilot.com, so was the setting for the server-domain. That way, the server could set cookies but being at ardupilot.com, it couldn’t read them back. I made the following changes:
Cookie domain: .ardupilot.com (was wiki.ardupilot.com, the “.” means “all subdomains allowed”)
Cookie name: apmforum (less cryptic-easier to debug)
I did some tests and my result is:
SID appears on login screen and after login redirect. That seems unavoidable but I’m still researching that and comparing with my own forum, because in my forum I don’t have that.
After that, it disappears, when clicking on any arbitrary forum link. I also tested closing the forum without logout and re-entering it after restarting the browser via a bookmark without the SID and for me it works. You might have to delete all board cookies before.
The SID is still persistent in MCP and ACP. IMHO, it shouldn’t be. I have to do a bit more research on that because again, in my phpBB3 installation, I don’t have that.