The tracking - of people and of what posts you've read or not, etc. does seem erratic. I think it gets re-booted at random times, and often forgets some things when that happens. Every now and then it discovers I missed a post from last March or something.
Anyhow, I have to re-log in every now and then, and remind it to remember me. Also - I'm not sure - but you may need to allow cookies for this site. It's the computer equivalent of re-flowing the solder joints!