AdamRynarzewski-4199,
How are you trying to access the App Service? Over private endpoint
What is the client making the call to App Service? Another App Service?
Is your WebApp on Windows or Linux plan?
--You may leverage App Service diagnostics from Azure Portal> Navigate to your App Service app in the Azure Portal. (screenshot below)
-- In the left navigation, click on Diagnose and solve problems
and search for “VNET”
--Use Regional VNet integration and VNET integration detector to fix any VNet integration issues.
and also leverage " Network troubleshooter"
See this doc: Troubleshoot virtual network integration with Azure App Service, to isolate the issue.
Kindly let us know how it goes, we will be more than happy to assist you further.