Thread:Project:Support desk/MediaWiki sessions and cookies not working on multi-server behind CloudFlare/reply

I'd use developer tools to see the names of the cookies being sent by MediaWiki, for example, inspecting HTTP request headers and seeing the names of the cookies present in the  header, and see if they actually make sense for what you have configured.

It may be that cookies never get sent to the browser, or your cookies never arrive to the server, but I doubt cloudflare would filter them.

Anyway, set also a debug log as explained in Manual:How to debug, since it will also print the headers received from the client, including cookies, so you'll see from there if cookies are being filtered by the load balancer/CloudFlare, etc.

Having multiple servers could cause issues: if server A generates a token and session, and on the next request, the client is being handled by server B that knows nothing about the tokens and session generated by server A. In this scenario, session.save_path should be in a shared directory between all instances, if the load balancer is not smart enough to send clients always to the same server.