That kind of scale is no problem for lighttpd, that's actually a low load. Whether you make 12 requests or 1 to the portal page, it shouldn't matter. Make sure your other resources in the page aren't generating redirects themselves. Also enable "Maximum concurrent connections" in CP so if there is some system out there making tons of requests in the background (usually malware) it's not trying to deal with potentially thousands of requests a second to a bot. The only thing I see on that crash is a 4 year old lighttpd bug that was fixed 4 years ago and long since fixed in our releases.
Support probably your best bet. One of us can check out the crash dump and track it down from there. If you go that route, include a link to this thread in that ticket for history.