After license downgrade (e.g. from Web Host Edition to Web Pro Edition), some domains/subscriptions are absent at Plesk > Domains or Plesk > Subscriptions or Plesk > Websites & Domains page
Note: Plesk can show Add Domain or Create Your Webspace page
The following warnings could be found at Plesk > Tools & Settings > License Management page:
Warning: Resellers management is turned off but you have several resellers(1).
Warning: Customers management is turned off but you have several customers(1).
Plesk does not display the domains and subscriptions belonged to nonsupported user types.
Web Pro Edition does not support Reseller management.
Web Admin Edition does not support Reseller and Customer management.