Re-add host deleted with the same hostname

I’am learning to use foreman. I just installed the foreman 2.0 via foreman_installer on a centos7. It works fine.
then I created a host with a puppet-agent-alpine docker image. it appears in the foreman. but after deleted the host, the foreman cant discover it again even recreate and resign the host. I need recreate the host with a different hostname.

I found an old question about this problem, it said just run puppet again. I did puppetserver stop/start, nothing changed.