To properly synchronize Assignee fields, we need to manually identify which user is representing the same person. E.g. we can have John Doe being named John in Jira and johnd in GitLab. Thus that getint.io is not able to automatically interpret, that this is the same person, especially that when fetching users, each app operates on different IDs. E.g. Jira Cloud uses some accountId hash while Jira Server uses username as id.