I've done some further diagnostics and am able to reproduce 100% of the time. If I browse from my mobile device (Android phone running Chrome Beta) it'll timeout after 3 or 4 pages. I am then not able to access amb.org from my desktop (wired all the way to the router) or laptop (wireless) for ~10 minutes.
mtr shows the following last few hops, and is the same for both when the site is okay for me and when it's not:
Host Loss% Snt Last Avg Best Wrst StDev1
22. 184.108.40.206 0.0% 6 150.9 150.8 150.7 150.9 0.1
23. 220.127.116.11 0.0% 6 150.7 151.0 150.6 151.3 0.3
24. 18.104.22.168 0.0% 6 164.0 179.1 164.0 253.6 36.5
When I cannot access the site I can see SYN packets leave my border router from browser requests and if I try to start a session from the firewall using nc to port 80. I do not see a returning SYN ACK. The conntrack table doesn't show any established connections to 22.214.171.124, just a bunch of time waits and the SYNs that aren't getting a reply. Tapatalk doesn't work on the AMB forums either during this time and I can browse other sites just fine. If I drop and re-initiate my PPPOE interface, which gets me a new IP address, I can browse the site again after 30 seconds or so.
When I can access the site, the SYN ACK comes back around the 200ms mark, in line with what the traceroute is saying.
It's as if my IP is getting blocking IP due to something the mobile browser is doing.
I'll do some packet dumps of the mobile browser traffic tomorrow and see if that shows anything interesting.