When uploading facts for a non-existent host, we seem to create a new host, but save it after importing its facts. This opens quite a large window during which additional fact upload for the same host could happen.

Reproducer details (assumes running on a foreman machine foreman-ansible, although it is reproducible with anything that uploads facts):

# playbook.yml
---
- hosts: all
  tasks:
    - setup:

Run with

for i in `seq 5`; do
  sudo -u foreman-proxy ansible-playbook -i ,duplicate-host -c local playbook.yml &
done

On my machine, this managed to create anything from 1 to 5 instances of duplicate-host.