Why are my sleep apnea events increasing.

Welcome @alm1952, There can be many causes for a sudden increase in AHI events. I don't think it's unusual for this to happen as myself and I'm sure others have had similar experiences. You might want to scan through the following discussion to learn what others have shared..

-- How to reduce my events while using my Cpap: https://connect.mayoclinic.org/discussion/how-to-reduce-my-events-while-using-my-cpap/

Here's an article with some suggestions that may help:
-- How to Improve Your AHI Score Overnight: https://www.thecpapshop.com/blog/how-to-improve-your-ahi-score-overnight/

My numbers can increase quite a bit if I sleep on my back vs on my left or right sides. Has anything changed in your sleeping habits?

John has answered you with helpful information and links. I believe he is correct suggesting that your sleep morphology, or even your physical morphology, is what has caused the change, even if they happen to be temporary....say a bit of sinusitis, inflammation somewhere along the air tract, new favourite sleep position (on one's back is generally not good, even if it feels great to awaken in the morning in that position), and so on.

You say your mask fit seems to be good (no major leaks that overwhelm the machine's fan's ability to compensate with more air volume), so we might be able to rule that out. Do you sometimes awaken with a dry mouth? If so, you are opening your lips, or you jaw sags, especially when on your back, and you won't get the therapeutic benefit that way. I, and many other CPAP users, have had to resort to taping over our mouths when we sleep because of this.

If you are on your back at times, a very common problem is that the chin sags toward the chest, pretty much thrust down there, by the pillow. This can close off, or constrict, the air passages in the throat behind the tongue, and you will get apneic events that way. Some people have to use a soft foam cervical collar, the kind you are asked to wear if you sprain your neck. They can be ordered for just a few dollars on amazon, more expensive at medical supply outlets where you get things like walkers, bed pans, and so on.

There is other help on line, much better than anything I can offer. If you go to apneaboard.com forums, register, and then explain your circumstances, there are highly knowledgeable people there who will help you to improve your therapy...hopefully.

Lastly, if you are averse to seeking help online, and I could certainly appreciate that, what's left might be another titration....the process of determining what you need, now, this year, for therapy to be effective. Things change, and sometimes not for the better. An overnight sleep lab might be in order, especially if you've never had one and only had a take-home device to verify if you have sleep apnea. A polysomnography, in the right hands, and interpreted by a good sleep specialist or respiratory therapist, might reveal that you require significant modifications to your machine's settings....OR.....that your machine is the wrong type for what you have now in the way of sleep apnea.

@alm1952
Do you have any neck pain/stiffness, daily headaches, and/or arm weakness/hand numbness? Do you have any changes in handwriting, bladder control or walking/balance issues? You may want to see a neurologist for small fiber neuropathy skin punch biopsy which can be linked to autonomic nervous system function and breathing. You may also want a MRI of brain/cervical spine to see if anything can be linked to your symptoms and increased sleep apnea events. Your cpap may also need pressure adjustments and an updated sleep study.