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 . 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?