Cannot delete a contact in Outlook.com

I have a contact stored in my Outlook.com account which cannot be deleted. The contact is visible both in Outlook and Outlook.com. When I try to delete the contact in Outlook.com, I receive the message "Couldn't delete contact" / "Nie można usunąć kontaktu". The contact is not present in my iPhone contacts, so it does not appear to originate from iOS contact synchronization.

I have also tried deleting the contact directly from People / Contacts in Outlook.com, but the problem persists.

Could you please check whether there is a corrupted or orphaned contact record in my Outlook.com mailbox and assist with removing it?