ElasticSearch keeps only a single document

Dear community,

I've been trying to build a simple ES index from a PS query in Campus Solutions vanilla PUM 17. I am pulling content from the course catalogue table via PSQuery - added drilling url / date field:

And the query returns results fine:

But after I build a full index, I keep on getting only a single value:

In Kibana, I see a similar pattern - only 1 doc shows, with the rest marked as deleted:

Is it an RTFM case and I am missing something simple? Any help is greatly appreciated.

Thank you!