Can you check how big cookies Cloudflare Access is using? Would clearing the browser cookie before accessing or using the InPrivate window solve this problem?
Did you add the client_header_buffer_size parameter to the nginx profile as described in the topic? Does it work?
If it passes an invalid and large cookies, nginx may take a lot of time to process it. This can cause your access to be slowed down.
Just tested on incognito mode.
I am sorry but the problem seems to be not exactly on max-cookie-size.
There is a redirection loop.
May I ask if the built-in Nginx handles HTTP to HTTPS redirection, if URL (instead of IP) is used?
Could I “tail” the access log anywhere?