Unable to create subdomain or slow creation via Plesk graphical interface: Please wait message is spinning continuously until Plesk session is expired.
In some cases, depending on server resources, the subdomain is created after ~20 minutes.
#PPP-44951 “Significantly sped up the creation of subdomains.”
- Plesk Obsidian 22 October 2019 (Windows)
If update is not possible for some reason you may try the following