@Alberto_Umana That may be the root cause - I did some additional testing in a development environment and found that the difference seems to be Serverless compute vs All-Purpose/Job Compute clusters.

When I run the Notebook and Job via serverless compute, the JSON is formatted correctly.
When I run the Notebook and Job via an All-Purpose Compute (tested on a few different versions DBR 15.4, 16.0, 16.1, and 16.2 beta), or the Job via Job Compute, the JSON is formatted incorrectly.

I've been running the job via Job Compute because I was getting OOM errors and driver crashes when running the job via Serverless compute, but I might try to break up the job into multiple jobs to see if I can get Serverless compute to work for me.

All this begs the question - is this new result expected? Should I expect different JSON formatting results on different computes, or is this something that should be investigated deeper?