External image App fails deployment, App image succeeds

I am deploying a container to the App Platform as a web service.

If I deploy a pre-built image, the build is obviously skipped, and the deploy stage fails usually[^1] with:

ERROR failed health checks after 1 attempts with error Readiness probe failed: dial tcp 10.xxx.xxx.xxx:8080: connect: connection refused

If I deploy with a GitHub repo (the same Dockerfile), the build is obviously not skipped, succeeds, and the deploy stage succeeds.

The only thing I am left trying to debug is the externally built image is for the wrong platform, but DO recommends linux/amd64 which is what it is built for.

Repo: https://github.com/freeCodeCamp/exam-creator/tree/4713a42e8ba966307d8ab62986b489bf28cbe13d

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[1]: Sometimes the deploy logs fail with just []