Hi Mark,

Can you try enable the app service logs

And check the log stream for any logs that may indicate why the application fails to boot.

You can also check the Application Event Logs to find errors related to starting your application:
 

Hi Anne,

After enabling the app service logs, the same 500 error is shown: 

HTTP Error 500.30 - Internal Server Error</h3><h4>The page cannot be displayed because an internal server error has occurred.</h4></div><div class="content-container"><fieldset><h4>Most likely causes:</h4><ul> <li>IIS received the request; however, an internal error occurred during the processing of the request. The root cause of this error depends on which module handles the request and what was happening in the worker process when this error occurred.</li> <li>IIS was not able to access the web.config file for the Web site or application. This can occur if the NTFS permissions are set incorrectly.</li> <li>IIS was not able to process configuration for the Web site or application.</li> <li>The authenticated user does not have permission to use this DLL.</li> <li>The request is mapped to a managed handler but the .NET Extensibility Feature is not installed.</li> </ul></fieldset></div><div class="content-container"><fieldset><h4>Things you can try:</h4><ul> <li>Ensure that the NTFS permissions for the web.config file are correct and allow access to the Web server's machine account.</li> <li>Check the event logs to see if any additional information was logged.</li> <li>Verify the permissions for the DLL.</li> <li>Install the .NET Extensibility feature if the request is mapped to a managed handler.</li> <li>Create a tracing rule to track failed requests for this HTTP status code. For more information about creating a tracing rule for failed requests, click <a href="http://go.microsoft.com/fwlink/?LinkID=66439">here</a>

I have also attached the whole log.

Anything in the Application Event Logs?

There are multiple errors in the Application Event logs. I got the same error in the CMD when trying the indicium.exe command. But, as far as I know, there haven't been any changes that would denied access.