Issue Summary

When a user is removed from a site, in the backend, there are still records due to content association. When the user is readded to the site, the account is "reactivated" in the backend and the content is reassociated as well.
If you try to delete a user, that have passed through this process, using the endpoint DELETE /rest/api/3/user, it will throw a 400 error.
If you try to remove that user from a group using the API DELETE /rest/api/3/group/user, Jira will throw that the user doesn't exist.

Steps to Reproduce

1. Create a user and remove it from the User Management;
2. Readd that user to the site;
3. Run the APIs.

Expected Results

Jira would either remove the user or show the error that the user has comments, issues reported, or assigned to that account.

HTTP/2 400 
server: AtlassianProxy/1.15.8.1

{"errorMessages":["Cannot delete user 'test' because 40 issues were reported by this person.","Cannot delete user 'test' because 5 issues are currently assigned to this person.","Cannot delete user 'test' because they have made 9 comments."],"errors":{}}

For remove from groups, Jira should throw a 204:

HTTP/2 200

Actual Results

Jira throws a 400 error without any "errorMessages".

HTTP/2 400 
server: AtlassianProxy/1.15.8.1

{"errorMessages":[],"errors":{}}

Jira throws a 400 error with the following error message:

{"errorMessages":["An error occurred: com.atlassian.idp.client.exceptions.UserNotFoundException: {\"schemas\":[\"urn:ietf:params:scim:api:messages:2.0:Error\"],\"status\":\"404\",\"detail\":\"A user with USER doesn't exists\",\"errorType\":\"UserDoesNotExist\",\"message\":\"A user with USER doesn't exists\",\"data\":\"USER\"}"],"errors":{}}

Workaround

• Remove the user from the UI.