I have a similar observation. My APP broke so I got them replaced in the store and I noticed as they updated to 4E71, the ANC was weaker. I used to listen to audiobooks whilst cooking or washing dishes and I wouldn’t hear the extractor or the tap running. After the update I started hearing those sounds. I started hearing cars outside my house and even birds singing. I thought the replacement was defective so I brought it back to Apple and the staff member has put them in their test machine, which showed they are to spec. She tried the store ones and then mine and noticed a big difference too. I got another replacement and when I got home it was same result. Weak ANC. At this point it’s statistically “impossible” for them to be broken ergo the software update made them worse. I presume the ones used by staff in the store were not yet updated to the newest software, hence theirs still had better ANC.
I have a suspicion Apple has re-tuned it for different sounds and frequencies or at least made them “leak” more sound when no content is playing… perhaps for safety reasons, perhaps to help with APP 2nd gen claims of being 2x better in noise cancellation. ANC does work very well when content is playing, even very quietly, but it’s not as amazing as it used to be when no sound is playing.