Apple released iOS 17 to the public a few weeks ago and you don't need to buy a new iPhone 15 or iPhone 15 Pro to get it. The update can be installed on a wide variety of models starting with the iPhone XS, and it seems that some people who have put it on their phones are now experiencing some strange Wi-Fi issues. What's more, the problem isn't limited to iPhones - some people with iPads are also reporting similar issues with iPadOS 17.
The problem, which doesn't appear to affect everyone, appears to cause a couple of main issues. Both of them can be highly irritating and problematic for those who are affected and, to date, there doesn't appear to be a proper fix.
The main issue is that some people find that their iPhone or iPad simply stops working on Wi-Fi. It will remain connected, but no data is transferred as if the connection to the internet has failed. However, users report that other devices connected to the same network continue to work as normal - and connectivity is often restored of its own accord, too.
Others report that while they can continue to use Wi-Fi, it can become extremely slow for a period of time. Again, other devices aren't impacted which suggests this is something specific to the iPhones and iPads in question.
Right now we haven't come across any real fix for this other than just letting the iPhone or iPad sort itself out and once it does, things should return to normal. One possible fix is to enable Airplane mode and then disable it again, so give that a try if you're afflicted with this issue.