I have APEX 24.1 running perfectly well on an instance of Oracle Always Free ADB 19c. I have then created a full Clone from database instance using OCI console, choosing Oracle Database 23ai as the destination, following these instructions. The upgrade seems to go well, I can access the new database using Database Actions as well as using SQL Developer just fine. I can also access the ORDS landing page, and can launch APEX from the landing page or from APEX Instance Details page.

However, when I try to login to either APEX Administration Services or the workspace, I get Not Found, HTTP Status code 404.

I have repeated the above procedure about 4 times now, and each time I'm getting the same result. I have searched this platform and elsewhere where I saw some advice relating to the ORDS or APEX HTTP error code 404 where the advice is to look into ORDS access logs, but these are not available on ADB just yet.
Any thoughts on this issue? Am I missing a trick somewhere?