Database backup in Plesk fails because of missing MySQL user: The user specified as a definer does not exist

Symptoms

• A backup creation fails with the following error in Plesk interface:

  PLESK_ERROR: Warning: mysql “dbname”
  Not all the data was backed up into /var/lib/psa/dumps/domains/example.com/databases/dbname successfully. Total space: 18.00 GB; Available space: 11.00 GB; Mounted on: /. mysqldump: Got error: 1449: “The user specified as a definer (‘old-dbuser’@’%’) does not exist” when using LOCK TABLES

• Unable to export MySQL database dump going to Domains > Databases > dbname…