Filebeat putting in thousands of extraneous fields

I'm trying to use the transform functionality in Elastic Cloud (7.8) and it is complaining that Filebeat has too many index fields (3700+ vs a maximum of 1024).

I've tried changing the fields file to send something different, I have deleted the templates and mappings and everything -- but all of these extra fields keep popping up. Any ideas?

What sort of fields are you seeing?