Android device does not display Google contacts in correct sort order

I cannot get Google Contacts to display my contacts in alphabetical order sorted by surname, with surname shown first. The problem has existed since about a fortnight after I bought the phone almost a year ago although the operating system and the Contacts app have obviously been updated since then. I'm currently running Android 11.1 (Oppo ColorOS 11.1) with (Google) Contacts 3.41.1.361694705 . The settings show - Display -> Sort by -> Surname - Name format -> Surname first - Edit contacts -> Default account for new contacts -> Device ... but despite the settings, Contacts shows surname first (as wanted) but always sorts in first-name order! This is true whether I access Contacts directly, or though the Phone interface. Curiously, if, from within Signal Messenger, I go to attach a contact card to a Signal message, then Contacts displays the contacts correctly (i.e., in alphabetical order by surname, with surname shown first). And just to be clear, this is ***not*** the Signal Messenger contact list I'm talking about here; this is the complete Google Contacts list. What is the likely cause of the problem? Is this a well-known bug? Where is the sorting done? On the device, as one would hope, or by having Google do it?