@AX, Firstly, Apologies for the delayed response. Based on the issue description, I understand that you are experiencing a 404 error for your WordPress site hosted on Azure Web App.
If you haven't done, you may leverage App Service diagnostics from Azure Portal> Navigate to your App Service app in the Azure Portal.
In the left navigation, click on Diagnose and solve problems
- Review - “Configuration and Management and “Availability and Performance” options.
Kindly ensure that the required file content is available in the root. On App Service: The wp-config.php files can be updated using either Kudu console or FTP Client (such as FileZilla).
- Browse to Kudu : http://”yoursitename”.scm.azurewebsites.net.
Example: if your Azure App Service Web App name is “testwebapp”, then surf to http://testwebapp.scm.azurewebsite.net
- Click ‘Debug Console’ and select ‘CMD’ : Traverse to
wwwroot
folder - For WordPress, update
wp-config.php
-make necessary changes, and save.
Kindly let us know, I'll follow-up with you.