I seem to be having this problem also. When I get a PushSubscription in Chrome, Edge, or Firefox (on a desktop computer), it seems to work fine. But when I try it on an iPhone or iPad (running iOS/iPadOS 17, so it should be supported), the PushSubscription will work for a bit, and then the subscription will somehow be lost. So notifications stop coming in, and the user has to register for anther PushSubscription.
I wish I knew why this happens and how I can fix it.