That's the limited cycles on the site, hence the database errors etc likely it is spammer bots and other crap traffic that is not real people wasting the sites cpu cycles. I am sure most site traffic these days are spam bots or other script traffic looking for exploits and other improper access. Just look at how often spammers register on SFM and post crap all over. Even small closed forums get hundreds of sign ups that are just ghost members. The database errors seem to be their worst around 3~5am PST but seen it get bad during the day as well comes in pulses and usually clears up in 20min.
The topic of this thread though is just a issue of needing to clear cookies or change whatever cookie management you have to allow longer settings or allow cookies to be set based on url. IE anti tracking cookie scripts often cause these sorts of issues. Also make sure to just click remember me and if all else fails get a cookie editor and change the time out to the year 4560 and set the cookie to read only.