We also still have some sync issue with EAS on mobile device.
As an example, I've recently setup an EAS account on an Android device (Using the built-in Android app).
When I open the app, it doesn't sync the mail folders. It keeps saying the sync is in progress but nothing happens.
I have to send an e-mail from the device (that is finally not sent at all) but it triggers the sync and it is working.
Still after this I've noticed that the Contacts are never sync'ed. It says something like "There is no contacts for this account".
Here I also try to create a contact from the device and store it in the EAS account. It appears on the device but is not sent to the server.
I know EAS should now be restricted to mobile devices and not used anymore on recent Desktop Outlook clients, but even with mobile devices, there are issues that we can't reproduce on real Exchange servers or even on open source server products that provides EAS (like for example sOGO).
So it seems that these are server side EAS implementation issue. Snifff.