So, I've looked thru documentation and this seems to be very odd problem.
If I create an appointment in D365, it syncs to Outlook Calendar/Appointment as expected. I can edit this D365 created appointment in Outlook, and it syncs (15min) as expected back to D365. All good so far.
Our Sales folks stay in Outlook and Track Email and Appointments using D365 App for Outlook. Email's tracked in "D365 app for O" properly track to D365 /Timeline as expected, Appointments do NOT track / show in D365 Timeline as expected.
After double checking all settings and etc., I've notice in the D365 App. under Tracked Regarding, we have "View Appointment" and "View in D365". Notice in the screen shot below, this is the Outlook created Appointment, selecting View in D365 has no data populated???? Same issue for View Appointment. If select "View Appointment" or "View in D365 for an appointment that was initiated/created in D365, both "View Appointment" and "View in D365" have all the data populated as expected!
So, it seems the "Track" for an Appointment in Outlook, does not properly define the Appointment data for D365, the data is blank!
Where would the D365 app for Outlook possibly be misconfigured?