I have the same Problem. I logged in Yesterday and let the Browser open, then this morning i had to relogin, so i clicked on Login ...:

Request

POST /login HTTP/1.1
Host: community.nodebb.org
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:34.0) Gecko/20100101 Firefox/34.0
Accept: /
Accept-Language: de-de,en-us;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
x-csrf-token: JeYKg0SP-ogi0oId5I25LmkFrIuFH6GAiJho
X-Requested-With: XMLHttpRequest
Referer: https://community.nodebb.org/login
Content-Length: 73
Cookie: express.sid=s%3AJbfGk0kTbgSsJRCOsYYRPCbqpj1om1Vq.4leOFMahMtak8WYv5j4WwwP779LhpsjenK%2Bnbskz6T8
Connection: keep-alive
Pragma: no-cache
Cache-Control: no-cache

Parameters

username=Nifty&password=xxxx&remember=on&returnTo=search%2Fno%2520login

Response

HTTP/1.1 403 Forbidden
Server: nginx/1.4.6 (Ubuntu)
Date: Sun, 14 Dec 2014 07:56:47 GMT
Content-Type: text/plain; charset=utf-8
Content-Length: 9
Connection: keep-alive
x-powered-by: NodeBB
X-Frame-Options: SAMEORIGIN
Vary: Accept-Encoding

Body

Forbidden

I had to reload the Page (F5) to get into.

Community

Nifty