It's because after upgrading OS 14.1, iPad will let you choose the authority option again.

Please go to setting and find the ATEN OnAir app.

Then check if the Local Network in the "ALLOW ATEN TO ACCESS" is disabled or not.  

If it's disabled, please enable it.

If it doesn't work, please uninstall ATEN OnAir app and reinstall again.

When you execute the app, the authority pop-up message will appear.  Please choose allow for the option of local network.