iCloud account duplicated in Contacts.app
I've had this annoying bug in Contacts app since updating to Big Sur: my iCloud account appears twice in the the Groups bar, and all contacts are shown twice. The contacts aren't duplicates, though - deleting either of them will result in the iCloud contact being deleted. This only occurs in the Mac app; iPhone, iPad and web apps aren't affected. However, the birthday calendar in Calendar.app shows duplicate birthday entries.
I've tried disabling iCloud contacts, rebooting and re-enabling, and also deleting all contacts on my Mac and then restoring from iCLoud - all to no avail. Has anyone got any ideas?