I bought my AirPod Pros the very first day and the large tips fit perfectly. I passed the seal test easily and the ANC works AWESOME! After a few weeks I noticed that the left ear seal was not as good as it was at first. I tried the medium tip and it was worse. Over the last few weeks the fit got worse and worse and the ANC barely worked because of all the sound leakage in my left ear. The right ear still worked great, perfect seal. I tried the fit test again and there was no way for me to get the left ear to pass but the right was good. Now I can’t even get the right ear to pass but it still seals well.
I just went to the Apple Store and got new large tips and the seal is back on both ears but the fit test doesn’t pass on either. I think there are two problems. First, the tips just degrade. I wear my AirPod Pros a lot including occasionally while I sleep. I noticed the left ear fitting worse and worse over a couple of weeks. I put the new tips on and instant fit but I’m sure they will begin to change over time. Second, the fit test has issues. I don’t really care if it works or not as long as I get a good seal. ANC is worthless if there is sound leakage.
I really feel that a foam tip would work way better and stay a good fit. Hopefully Apple is getting the message.