Cannot create a check-in because the system does not detect an assigned manager

Summary:

For some users - but not others - the system prevents the user (the HR administrator, the manager, and/or the user) from creating a check-in. Specifically, the template dropdown is blank and the following error message appears in the check-in screen. It seems to happen in cases where the user's supervisor changed recently - but, again, it's not consistent - it works for some of the members of the same team but not others.

I can confirm that the user has an active manager of type Line Manager, that they are assigned to a position, and that they are eligible for the check-in.