nevermind, this is when upgrading from 6.1 or 6.2 to 6.3.4 apparently. Missed that distinction.
The release notes mention this on page 12 (After You Upgrade):
To reduce downtime, the default upgrade behavior will now back up Log Database and Access Tracker
records but will not restore them as part of the upgrade. If required, you can manually restore them after the
upgrade through either the application or the CLI. The session log database contains:
Access Tracker and Accounting records
Event Viewer
ClearPass Guest Application Log
and then goes on to tell how to restore these.
When I checked after upgrading however all my access tracker data was still there and no file could be found in Administration > Server Manager > Local Shared Folders.
So whats the deal here? Was this 'feature' left out or why am I seeing different behaviour from our system?