While I’m not denying there is racism involved in some quarters (the tweet you mentioned being one obviously heinous example), the discomfort for some of us comes from the use of the Queen’s very special, very intimate nickname, and our lack of knowledge about whether she gave her blessing and how she feels about it. The only person left who called her that was Philip and he just died. So hearing her nickname is possibly raw and tender for her. And maybe the gesture of naming baby Lilibet is beautiful and tender and healing, or maybe it pokes at the pain. And there’s no way for any of us to know.