I’m thinking that your site just built up a resistance to absorption. This happened to me many years ago and I kept bolusing through the pump with zero effect on blood sugar. Then, finally, the insulin dam burst and my blood sugar plummeted. Unfortunately I was busy in the dentist chair during the period I might have sensed what was going on. This was before the I used a CGM or a hypo-alert dog. The consequences were severe and I was lucky to survive.
I think as soon as you observe a slowing of the usual effect of insulin lowering BGs, I would switch to syringe corrections and frequent monitoring, especially with fingersticks.
I tried the Omnipod back in 2012 for five months. I had a poor experience and you may read about it here. I recognize that Omnipod use has been successful for many, unfortunately it didn’t work for me and I had several occurrences like you wrote about here.
I think fading sites are hard to make a good timely judgment on. I’ve been tempted to switch out a site and just before I do absorption returns to normal. I think it’s much better to switch out too quickly than too slowly. I know doing it too quickly risks wasting insulin and supplies but I think my health is more important than that.
Lastly, you mention that poor absorption happens about 10% of the time for you. Have you tried some new places on your body? Since I switched to infusion sites on my back this has not happened to me. Good luck – glad you are safe.