ECS Fields are not mapped properly in package mappings

We have defined in ecs.yml in our fields directory, but they are not reflecting when we install the plugin into Kibana:

- external: ecs
name: vulnerability.id
- external: ecs
name: event.id
- external: ecs
name: vulnerability.result
- external: ecs
name: vulnerability.reference
- external: ecs
name: vulnerability.score.base
- external: ecs
name: vulnerability.score.version

Highlighting "vulnerability.score.base", which should be a float under ecs, is being mapped from our plugin as a keyword field instead:

I'm not sure if this is a bug or just a misconfiguration but any help you could give us would be great!

Just for quick reference from the ticket:
https://www.elastic.co/guide/en/ecs/current/ecs-vulnerability.html

Start with ecs.yml in the fields directory and trace how package mappings are produced when the plugin is installed into Kibana. Compare the declared ECS types with the resulting mappings; done means vulnerability.score.base is mapped as a float and the listed ECS fields resolve to their intended types instead of keyword.

Written by the indexing model from the issue text.