Does your Router utilise an Access Control List (often implemented via a list of Physical MAC Addresses of WiFi Client devices) that restricts access to 2.4GHz or 5GHz radios - or perhaps has QoS features that similarly restrict network bandwidth? If so, this may explain the behaviour that you observe.
If these features are not employed by your WiFi Router, the symptoms that you describe suggest that your Router may have an issue with specific WiFi client devices. If so, this might be easily be resolved by a restart of your router.
To restart you home router, disconnect power - then wait at least 30 seconds before restarting. When you router has rebooted (which may take several minutes), force-restart your iPad:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.
A further measure, worth trying, is to reset the Network Settings on your iPad:
Settings > General > Reset > Reset Network Settings
I hope this guidance proves to be helpful in resolving the problem.