If I deselect and reselect the calendar is does not force a sync for user A. So the folders may just force a sync when you select and deselect for user B.

I tested with a different user in the environment and her shared folders synchronization times were in real time for the same users we tested with with user A, but she does not leave the calendars also selected like user A. But at random times it will sync, I cant get it to behave consistently. Mail settings are set to download instantly. For this user if I right click and look at the synchronization status its about 6 hours behind, If I open and close outlook it maintains the same, hitting send and receive all does the same. What they see is an entire list of shared calendars and they can toggle which ones they would like to see. When I mean real time I mean when you view from right click and sync status on that users calendar. (The download shared folders option is set correctly). To be 100% honest I am not sure how they are supposed to behave, but it seems to be like they are supposed to be in real time. They have shared calendars in which everyone can see.

I would like to mention I would really not like to rebuild her profile or re create her ost file. They are using office 365 exchange is also NOT on prem. Absolutely nothing is on prem everything is hosted in azure. Consist of 3 Windows Server 2016 remote desktop servers we are using UPDS.

Microsoft online calendar sharing