When migrating via JCMA. The UI may prompt the user with the message:
"We couldn't check for duplicate users"
The summary state:

This is usually related to problems with the projects these users appear in. View the checks for the data preparation below....

However, all the data preparation checks are marked complete . The UI message is misleading because the user can't easily identify the problem.

When the user tries to migrate, there are error logs such as the following:

2023-08-04 14:25:48,672 pool-71-thread-1 ERROR yb1012 865x256x2 pqoq47 10.45.216.229,0:0:0:0:0:0:0:1 /rest/migration/latest/check/123abcc5e7d1baf9e669f343245ce858be8fb52f7 [jira.migration.log.ExportLog] 2023-08-04 14:25:48.671 ERROR ACME project-export Group reference could not be found. [JCMA 133] Details: Workflow [My Test Workflow] with id - [Undefined] has missing reference to group - [jira-user-admins-group].

In this example, the issue is related to a workflow that contains a reference to a group that was deleted. JCMA should provide a clearer error message pointing to the problem with the workflow or project data instead of displaying a warning related to the "duplicate user check".