What is current network connection type (wired/wireless/USB tethering/WiFi Direct) on your Windows 10 and iPad?
Could you please check on your primary machine if spacedeskService is running?
Just run services.msc, find spacedeskService and check the status.
What is the current network profile on your primary machine? Is it Private or Public?
If you are using wireless network, are both primary machine and iPad device connected on the same wifi network with the same network band (2.4Ghz or 5Ghz)?