Enabling the synchronization on a workspace / folder does not always trigger the rootRegistration event

Steps

The only step is to enable the synchronization on a workspace or a folder.

Actual Result

For some user on some sync root, the rootRegistration event is not triggered/generated. There is nothing the the document history and Drive receives no events.
For instance, this document will reproduce the issue with the yachour userID. But with my account, it works at 100%.
We know it happened for other users on the intranet and on another customer server.

Details

The exact date is 2018-04-13 between 10:20 and 11:30 (as you can see in the document's history: actions from mschoentgen userID).

Expected

The rootRegistration event must be triggered and sent back to Drive.