Participant API get_individual_metadata_template_for_seqr endpoint broken

The API endpoint get_individual_metadata_template_for_seqr seems to be broken, specifically the returned headers are empty.

Steps to reproduce:

Go to the API endpoint in Swagger /api/v1/participant/{project}/individual-metadata-seqr Get Individual Metadata Template For Seqr
Enter a dataset name and leave the response type as json.
Observe that the rows and header_map components of the response are correctly populated, but the headers list is empty
Change the response type to csv/tsv and observe that the response is totally empty, because these export types depend on the headers list.

The section in the participant layer where the headers are collected and returned looks fine to me, and hasn't been changed for a few years. Not sure why it's not working now, will do some investigating.

populationgenomics / metamist