To narrow-down/fetch more details on the error:
Leverage App Service diagnostics from Azure Portal> navigate to your App Service app in the Azure portal -to fetch more details on the error.
In the left navigation, click on Diagnose and solve problems
– Checkout the tile for “Diagnostic Tools” > “Availability and Performance” & "Best Practices".
Access Kudu - https://<Your app name>.scm.azurewebsites.net/ - to analyze logs and collect diagnostic dumps as required.