This is a weird one, and I've been Googling for days without any luck.
I have a client who runs Exchange/Outlook 2016. Jane Doe is in the Marketing department, and her AA (John Smith), and a few others in that department (We'll call them Jimmy, Sally, and Bob) cannot see her Free/Busy status (the entire row is grayed out) when in the "Scheduling Assistant" in Outlook.
However, if John goes into OWA, he sees everything perfectly fine.
If John views Jane's calendar through the normal shared calendar, he can see everything perfectly fine.
If I personally use Scheduling Assistant to create a meeting with Jane (using an account that is not Exchange privileged), I'm able to see her Free/Busy status in Scheduling Assistant.
This behavior happens even on a computer these users have never logged into before, so it's not an Outlook caching issue.
Permissions appear fine:
This is using get-mailboxFolderPermission Jane.Doe@contoso.com:\Calendar
FolderName User AccessRights
---------- ---- ------------
Calendar Default {AvailabilityOnly}
Calendar John, Smith {Editor}
Calendar Null, Sally {Reviewer}
I can't for the life of me figure out what's going on.
TL:DR: User in Marketing cannot see Jane Doe's Free/Busy status only in Scheduling assistant on the Outlook client. OWA is perfect.