Following the regular update of certificates on our IIS Application Request Routing (ARR) devices one of the redundant pair stopped accepting the new certificate. Due to this issue the ARR started to block traffic which caused web applications like f.e. Financials and Synergy to be unreachable. As the devices are a redundant pair not all end-users will have experienced this issue.
We observed the fault in our monitoring and when the cause was found the ARR was first taken off-line. then reset and tested. Which resulted in a stable service again.