[Answered ]-Django save() refuses to update an existing record

I would advise to update the querset in bulk, with .update(…) [Django-doc]:

from django.db.models import F

@database_sync_to_async
def increment_unread(room_id):
    RoomOccupier.objects.filter(room_id=room_id).update(
        unread_count=F('unread_count')+1
    )
    return True