I am in the US with a PSTN calling plan and a service # assigned to an auto-attendant. For the past few weeks, I've gotten a number of reports from people who've attempted to dial into that service number say it requires a few redial attempts before it connects/rings. I've verified that myself independently. I'd estimate it happens about 25% of the time. If you call back after a few moments, it usually then goes through and rings.
Any advice as to where to look to troubleshoot? The Call Quality logs don't seem to have record of these calls that I can find.
I think that you have to start a support case with Microsoft for this, I guess that the call of some reason is not routed into their infrastructure but they are the only ones that can check that. They will need an example of a call that didn't work with information of who called (phone number), when (date and time) and to what number.