Your profile lists a single pressure implying a fixed-pressure CPAP treatment, but you also list an auto-CPAP machine.
Assuming you are on single-pressure CPAP treatment, suddenly experiencing mouth leakage after years of successful usage is just bizarre. The "sudden" onset of apneas and hypopneas might be that your treatment requirements have changed sufficiently that your current settings are simply inadequate.
Assuming you are on auto-CPAP treatment, things might make a bit more sense. As above, it may be that your treatment requirements have changed as you have aged (it happens), or as a result of your sleep position, and that the pressure requirement (and supplied by the device) has recently increased to the point where your previous success in keeping your mouth sealed is being overpowered. As well, it may be that the pressure requirement has reached the upper limit of your auto-CPAP upper-limit setting. That last could allow apneas and hypopneas to again occur, resulting in your recent experience.
You might consider downloading the SleepyHead software and examining the recorded data on the SD card. That should tell you more about what was happening that night. Other than that, consulting with your doctor and possibly having another sleep study would also be worthwhile.