Update:
Following the info on this topic:
I was able to make a quick fix by enabling “include secure categories in tag count” in settings.
But that same topic noted that this shouldn’t need to be enabled with this fix: All tags page is empty for non-staff users - #3 by JammyDodger
Maybe there’s a new bug?
For more reference, all of our categories are private so we can control access throughout. So all tags would end up being used in a “secure”/private category.