Manual enrolments of teaching staff (e.g. co-teachers, teaching assistants, course viewers) in Moodle expire in 30 days (from the day you enrolled them), unless you changed the enrolment period when you first enrolled them.
If your teaching team has reported loss of access to your module, click on Participants in the course page contextual menu (beneath the module name at the top of the course page):

Locate the staff member in the list of enrolled users and check whether their enrolment status is shown as Suspended.
If their enrolment has been suspended:
- Click the gear icon to the right of the staff enrolment.
- Change Status to Active.
- Next to Enrolment ends, make sure that the check box is ticked, then specify an appropriate end date.
- Don’t change any of the other settings.
- Click Save changes.