Sync broken: CSync failed to access

This sync issue is driving me nuts and keeping me from syncing my files.
It appeared after some folders were moved around (possibly copied and deleted.)

I’ve run sudo -u www-data php occ files:scan --all but it just finishes normally

Nextcloud version : Nextcloud 13.0.4
Operating system and version : ubuntu 16.04
apache 2.4.18-2ubuntu3.8
PHP version : 7.0

The issue you are facing:
The sync client cannot sync, it comes with error message: NTS/Onboarding clients/Loading Emails

Is this the first time you’ve seen this error? : it’s been there for weeks.

The output of your Nextcloud log in Admin > Logging: nothing related appears in log

When trying to navigate in the web interface to the path “NTS/Onboarding clients/Loading email” the browser is just redirected to the file root.

Did you find a fix for this?