The Denon HEOS app opens the Spotify app to connect via WIFI/LAN to the Denon DRA-800H. However, the Denon is not displayed and can't be chosen. Reset the Denon already. The problem is the same with MS Surface.
First thing you can try here is running a clean reinstall of Spotify on both your laptop and mobile. This will get you the latest app version with all necessary updates.
If this persists after the clean reinstall, restart your network and check if you observe the same when connecting to another network. If it works with a different connection, it's best to contact the service provider of the original network for more information.