There is an intermittent failure in the JSON tests. I can reproduce it in a few minutes with:
Attached two of the output files. It appears that in one case the JSON parser is leaving the results of a partial parse in the structured field, I see "structured" : "key" so looks like the JSON parser read "key" as a string before realizing it was not looking at valid JSON, but left the partial value behind. I think we talked about something like this before.
I'm not sure why they are intermittent but I would guess that it maybe depends on the content of the logs. The tests are using logs from k8s which are not a predictable format.