When working with the AI Noise Reduction badge, Processing omissions occur.

[koz___]

When working with the AI Noise Reduction badge, there are many times when an image (raw) that should have been selected is not processed.

[koz___]

It was a stack error, not a processing omission.
When I checked the local folder in the library, I found a processed DNG, but it was not stacked with the original image and had not been added to the collection.

[JohanElzenga]

Most likely you were in a smart collection, or had an active filter, that filtered out the returning DNG.