Actor runs do not store output in dataset on Apify

I have an actor that is working perfectly locally - storing output in JSON files in the default dataset - but when I run it on the Apify platform, the run shows no results even though run was successful and results were found.

I am attempting to store the results with:

I have also checked that the object is correctly produced using log.info(`Result: ${JSON.stringify(result)}`) and it is correctly logged out, so I would expect it to be stored.

Is there any way to debug this, since there are no errors?