Connection Timeout on Particular Websites.

Last night I started seeing a connection timeout problem with a few websites, although the list is growing over time. Some of these are pretty common sites like the Twitter link shortener t.co In other cases http version of a blogspot.com subdomain times out, but the https version loads immediately. DNS resolves on these, and all of these work from the upstream router. No error messages are recorded on the Fortigate, I can find no evidence of the traffic at all. However, one site connected long enough to do a redirect, and then it failed. I upgraded to 5.6.7 today and turned off all rules, but see no changes.  Any ideas?