External import does not update objects with user-type attribute

Issue Summary

External import does not update objects with a non-empty user-type attribute

Steps to Reproduce

1. Run the initial import with the External Import to create schema, mapping, and objects
2. Update an object type created in the previous step to add a user-type attribute
3. Update an object to set a value for this new user-type attribute (through the UI)
4. Go back to your external import and update the same object with data different from the initial import
5. Run the external import again

Expected Results

The object data will be updated via External Import

Actual Results

The object data is not updated via External Import and it throws an error similar to this:

Error: User(s) (<xxxxxxxxxxxxxxxx>) not found in Jira. [Object (Label: xxxxxxxxxxxxx, Id: xxxxx)].

Workaround

Remove the value in the user-type attribute and run the external import again

Notes

It also happened for Discovery Import