wikitech.w.o regularly looses session directly after login for me. I.e. the first page load after login has me logged in, then pressing reload leaves me logged out. I'm not checking the remember me checkbox. Logging in the second time makes it work. Though I doubt that has anything to do with it I use https://addons.mozilla.org/en-US/firefox/addon/self-destructing-cookies/ ; have cookies set to be deleted at the end of the session and not white listed any domain ending in wikimedia.org for cookies.

Maybe this is related to T115457.