Have you tried on different computers / browsers?
Just got it working. Or seems to be. Been stable for a bit now and the admin page is back.
Had to replace the URL of the site, with localhost:localport
I've just installed git version on debian jessie, after a while nodebb stop work and i've to restart it. I've checked log but i don't see anything that can help.
This is the current situation after a while i'm using it https://imgur.com/a/caC0ju2