Can not add contact group

[grapvar]

When I try to add a contact group in a stock Contacts app, I get «A group with that name already exists», regardless of the name I provide, in spite of Group list is blank. Screenshots attached.

Yes, this part of stock Contacts app works seamlessly for Local contacts and for Google Contacts.

I am at Xiaomi Redmi 6/Android 9/MIUI 11.0.5 (released 16 Sep 2020)