I'm having this problem as well (version 3.6). Everything was working great until, I believe, the update to the addon that added the summarizer feature. I've tried many various ways to get it to work (reinstall, using different steps to add the session token, etc.), yet it's still broken.
My temporary solution has been to paste and browse to my session URL, that includes an the authenticated session token, when starting the private session. That will make it work until all private tabs are closed.