cloud.domain.tld should display its own install of WordPress, independently of the WordPress installed at domain.tld.
To simplify matters, delete the sub server / sub domain and create a top level virtual server with the domain cloud.domain.tld and see if you get the expected results.
Somehow Safari is caching or doing something wrong. With Chrome it is indeed working fine
So I donโt think this is Virtualmin or Webmin issue, this is Safari Browser issue - but still why is it caching a subdomain as main domain - very weird behaviour