"disabling a problematic route that we found to be related to this"
It was not #DNS, it was #OSPF! (Or IS-IS?)
https://azure.status.microsoft/en-us/status
Check the current Azure health status and view past incidents.
And just after, routing is removed as a possible cause (like DNS was before) and "We suspect that an inadvertent configuration change as the trigger event for this issue.'"
PEBKAC as usual?
Stéphane Bortzmeyer