iCloud (CardDAV & CalDAV) Sync Hanging & Failing

iCloud Contacts (CardDAV) & iCloud Calendar (CalDAV) synchronisation now hanging/taking a long time to complete - window shows ‘Synchronizing folder list’ or ‘Synchronizing items’.
On occasions the process aborts/times out with the message ‘No Valid Licence’; which then requires a restart of eM Client in order to activate syncronisation once again!
At weekends the iCloud sync process seems to complete without delay.

Anyone on the forum or (better still) at eM Client Support got any idea what’s causing this problem and whether it’s being investigated/resolved or not?