@johnhans my prescription was also expired in July. I sent my sleep medicine doctor a message on the Mayo Patient portal and asked him if they could renew it. I told him all was going well with the CPAP and I wasn't having any issues sleeping. He replied that he would renew it for a year and then setup another appointment at that time to see how it was going.

I would ask him that since he is not able to see you sooner than the middle of September why can't he renew the prescription so you can get replacement mask (your previous one that he more than likely allowed) until you are able to get the appointment? I would think they would want to help you with any CPAP issue.