I'm in Canada, so different provider, and recently switched carriers - so it happened before and after. Also on 16.2 and 16.3 - so no clear pattern. I still have WiFi assist on currently.

Similar issue on iPhone 14 Pro Max and didn't get fixed with 16.3 update - Genius Bar noted it's because I have a VPN installed (which I don't believe) - at least I feel a bit of comfort that I'm not the only one experiencing this!

Their other recommendation was to reset all network settings - will see if that makes a difference