I didn't run into that issue. In fact, the revision was auto populated with the replica name. My guess is that your replica isn't in a good state. You can confirm this by checking the App Down or Reporting errors detector in Diagnose and solve problems blade. Furthermore, if you click on the Containers blade, and change your base revision image or activate a different one.
I also encourage you to use the Troubleshooting in Azure Container Apps | Microsoft Learn guide for basic scenarios that you're most likely encountering.