There is a scenario where the image caching logic incorrectly skips building a Dockerfile when that Dockerfile has an intermediate stage based on an image that has a cache miss. An example of this scenario is the this build (internal link). That build was triggered from this PR: dotnet/dotnet-buildtools-prereqs-docker#1207. In that PR, a change was made only to the crossdeps-builder Dockerfile. The build only ended up publishing that crossdeps-builder image and none of the images that are dependent on it.

Here is an example Dockerfile with such a dependency: https://github.com/dotnet/dotnet-buildtools-prereqs-docker/blob/642ddfa47486760a15781758c7e8c0709c4c96c0/src/azurelinux/3.0/net9.0/cross/amd64/Dockerfile#L3. The image caching logic only accounts for the dependency of the final image. In this case, the final image is based on crossdeps-llvm, which has not changed. So the cross Dockerfile never gets built. But it needs to be built because the content it contains is copied from crossdeps-builder, which has changed.