Page stuck on mobile site even in private mode

[yalag]

For some reason my safari on the desktop is stuck loading github.com mobile site. I can't make it go back to the desktop site even when I change the user agent, or go in private mode. I've tried clearing history, cache, data, and rebooted many times. How do I fix this?
Also, it's not a problem for other users on this mac. Also not a problem with other browser like Chrome.

 

[bogdanw]

Look in Safari Preferences - Websites - Reader. Sometimes sites are added there by mistake.