201-vmss-windows-app-gateway possible use one app gateway if vmss is in the same subnet

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[Template Name goes here](Template link goes here)

### Issue Details
I deployed two VMSS in the same sunet based on this template without success, is it possible use one app gateway if vmss is in the same subnet ? or should have two subnet in the same vnets ? or should have two app gateway for two different subnet in the same VNET ? Thank you :)

### Repro steps (*if necessary, delete otherwise*)
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No template file, test, or reproducible steps are provided. First identify the VMSS and application gateway template referenced by the issue, reproduce the reported deployment, and determine whether the expected outcome is a template change or a documented configuration answer.

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