Issue
When requesting clone, you will notice the 'Clone from' field is populated as 'Standby Database' automatically. If you click the exclamation mark besides the 'Standby Database', you will notice the 'War version' mismatch the version of the source instance
Please refer to the following screenshot as an example
Resolution
This version mismatch can be ignored. Standby Database field is deprecated as we are using a new Backup based clone engine, the content of this 'war' field will be assigned dynamically during the clone process