It seems that this is due to Planned network maintenance scheduled for Friday, October 1 at 01:00-04:00 UTC (Thursday, September 30 at 9:00 PM-midnight EDT).
This is a script for sending an email when users got comments at Stackoverflow. I had wished I could get an email when I got a comment at Stackoverflow. Although I investigated about this, it seems that I can get the email every 3 hours. For this situation, I wished I could get it much earlier. I thought that this can be achieved using GAS and Stack Exchange API. So I created this script.