I've been on a CPAP for many years, and when my old machine didn't make it down here when I moved 5 years ago I had a new sleep study and a new machine. I've been fine, but this past year my AHI went up a bit. I was notified of this when I asked the sleep doc's office to fill out the paperwork in anticipation of my FAA medical.
I replaced my headgear and the numbers started going down. I made some additional lifestyle changes and my numbers are good now, but so far I only have 14-15 days of consistently good numbers. The FAA normally requires that the numbers be good over a year for someone who's been on the CPAP for a while, but since it was an equipment failure and they did not tell me ahead of time, is there any chance that 30 consecutive days of good numbers (per the protocol for a new diagnosis) would be enough to convince them that we've fixed the problem and allow me a special issuance?
I use the device every night, and over 95% of nights are greater than six hours/night, well above the 75% requirement from the FAA.
There are many issues with PAP machine recalls that is creating issues for pilots who have or are trying to get special issuances. Just provide an explanation from your sleep clinic explaining the circumstances and provide at least 30 days of good data showing 75% or more usage during sleep periods, and six hours avg. use per sleep period. Once you get accustomed to the new hardware, the AHI should come back down and you will be OK.