I'm running the free version of Jira. Yesterday I added 3 new users to my Jira. Just a reminder that the free version allows only team-managed projects, so keep that in mind.
1 of the 3 users can create tasks/stories/anything but does not show up in the Assignee field nor in the Mention (@) list in every issue but the ones this user creates.
So, if I create a issue I cannot assign the issue for him because he does not appear in the list even after i type his full username. Yet, he can create and assign a issue to himself. And if I navigate to the issue he created, I can tag him and assign him only inside this issue.
Things I've checked:
- He appears as a user in board, list and basically every other menu (JF icon).

- He does not appear in the access menu.

- He does appear as a active member of the Jira product exactly like the others.

- His role and other settings are identical to the other two.
Things I've tried:
- Deleted him and invited again. Didn't work.
- Checked global permissions.
- Checked other similar questions and none were related to this kind of problem or did not solve it.
I don't know what to do anymore and how can I solve this.