@dunlix (and others)
Thanks, the disable plugins suggestion worked. Apparently it was the "sanitize html" plugging that was causing the problem.
Not even sure why we had that still installed.
Thanks all for the troubleshooting help!
I'm experiencing the same problem, yet I'm not using Apache or any other reverse proxy.
The forum is hosted on a remote VPS, and accessed directly from an IP address as it currently does not have a domain.
It didn't start right away, it worked normally in the beginning. Reloads and restarts don't help.
I have NodeBB 1.0.3 as well
Problem was solved by leaving blank the Cookie Domain field in Admin -> Settings -> Advanced