I didn't use the Silent Push fail device (15.3.1) for 1 day, and when I turned it on 1 day later, I didn't get the silent push again. There is no power consuming process that should block this silent push. On the other phone (16.5.1), it can still process the silent push even though I enter apps one after the other.

Silent push works consistently on iPhone Xs (iOS 16.5.1), but fails on iPhone Xr (iOS 15.3.1) with "Absolutely Must Not Proceed" in the console logs. Both devices are tested under identical conditions (no power saving mode, no another background apps, same configuration). Why would iOS 15 block the push while it works on iOS 16? Could this be due to stricter background task policies in older versions? How can this be resolved?