Haven't tested it fully yet, but iOS 17 seems to have messed up how iOS handles being on a Wi-Fi without internet. Previously when connected to the Poly in hotspot mode iOS would detect no internet and then use cellular for internet connectivity while still allowing AirPlay and UPNP on the Poly Wi-Fi connection. After iOS 17 is seems to no longer want to failover to cellular for internet connectivity (yes even with Wi-Fi Assist enabled). It attempts to use the Poly's hotspot regardless which of course fails.
I plan on testing it a bit more, but in the meantime the solution is to set a static IP without a Router configured. This will force it use cellular for internet (all the 0.0.0.0/0 routes) but still allow AirPlay and UPNP to the Poly (the 192.168.1.0/24 routes).
- Connect to the Poly hotspot as normal.
- Go to Settings -> Wi-Fi -> Click on the ( i ) next to the connected hotspot.
- Note your current IP Address.
- Change Configure IP to Manual.
- Set the IP Address to what it was previously.
- Set the Subnet Mask to 255.255.255.0.
- Leave the Router field blank.
- Click Save.
- Set Configure DNS to Manual.
- Add the DNS Server 192.168.1.1.
You should now be able to get to the internet over cellular while still being able to AirPlay and connect to UPNP to the Poly.
Will update once I test a bit more if it turned out to just be a one off. For now though, can confirm this workaround works well.