It appears that some users in Japan are experiencing difficulties accessing major global websites such as Amazon.com and GitHub from within Japan.
When accessing GitHub, etc., you get 502 or 503 errors. Sometimes you can access them, but most of the time you cannot.
There was an unexpected problem serving your requestThis situation is not occurring worldwide, but appears to be limited to Japan. Below are the results of an investigation using Google Trends - the number of searches for that error message has been increasing since September 11th.

Since it’s still rising, it seems the damage will continue to expand.
Hello. I access to Github few times in today.
In that accessing, I have some error as following.
There was an unexpected problem serving your request Please try again and contact us if the problem persists including FBA2:9F11:23B5E:340EC:5B97CB3A in your message
Or I have received 502 error some times as well.
I’m using Chrome browser. I opened the Github URL as a secret tab for excluding Github-related extensions. But this didn’t works as well.
I have any problem?
…I tried to send this, but I couldn’t even send it.
Accessible via VPN
You can prevent this error by accessing via VPN from the United States, etc.
I used hola VPN (premium).
GitHub is also aware of this problem and responding

September 11, 2018 23:20 Japan Standard Time We've identified the source of the exceptions and are working to address the problem.We have found the source of this problem. We are currently addressing this issue.
Sep 12, 2018 00:00 Japan Standard Time The status is still yellow at the beginning of the dayThis problem still has not been resolved today.
Got a reply from GitHub
I received a reply from GitHub a few minutes ago.
Sorry for the trouble! The team is working to resolve this issue now. Please let us know if you're still having trouble when our status is back to green: https://status.github.comThey said to check this periodically.