apap suddenly erratic

Have been using an icon auto apap machine with full facemask very successfully for about 4 years now.
Prescription setting is 10cm, but full range 4 to 20 set up on machine
Recently I have started snoring again, and both wife and I have been woken with air loudly escaping from the mask, and at that time I notice that the machine is strangely blowing at max pressure of 20 cm.
When I change the machine to cpap mode at 10cm, all is ok again.
Can anyone suggest why the apap mode seems to have become erratic/ why I have suddenly started snoring again in apap mode?

Let's start simple; how old is the cushion on the mask?
--Has your weight changed recently?
If apap wide open has worked previously, it could be the mask or a change in your breathing.
Have you seen a doctor?