The application alias "X" can not be converted to a unique application ID.
You get this error when two or more Oracle APEX applications have the same alias.
When you import the sample application in the same workspace and give it a different ID, the alias is changed automatically so it's unique. However when you import an application in a different workspace, the alias is not being replaced by a unique value, which might result in the error: "The application alias "X" can not be converted to a unique application ID."
There's an easy way to find where those applications are with the same alias by running the following query (as a DBA or a user with the APEX_ADMINISTRATOR_ROLE):
select workspace, application_id, application_name
where alias = 'X'
This will give you the workspace, application id, and application name with the specific alias.