It seems that the folders for subdomains are not being created as described in the Plesk documents.
Changes in organization of subdomain-related directories. Due to safety reasons, Panel now stores content and configuration of hosted subdomains in separate directories:
/<VHOST>/<subdomain_name>, the directory that contains HTTP/HTTPs documents (unlike the earlier versions that separated HTTP and HTTPS documents).
/<VHOST>/<subdomains>/<subdomain_name>, the service directory that keeps subdomain configuration
What we were expecting according to the document to happen was
/vhosts/sample.com/dev- created for the content
/vhosts/sample.com/subdomains/dev- created for the settings
However when we try to create a subdomain for a domain sample.com what we see happening is:
/vhosts/dev.sample.com- is created with the settings
/vhosts/sample.com/dev- is created for the content