Not a bug
I have set those monitors for one of websites
US-Dallasduring the weekend (July 18-19) and Monday (July 20) I had multiple critical notifications from US-Michigan as well single from other as Time Out when the site was up. I have expect to receive critical notifications when all each monitors will report incidents 3 times in a row and that will be escalates to critical level but not one single US-Michigan monitor will trigger it when all are show as successful and site is up. It is kind of annoying when I'm getting messages in the middle of the night or a conference and those failures are not valid.
Customer support service by UserEcho