Random Apple ID and phone number notifications

In the last two weeks I’ve received two different notifications saying “Your Apple ID and phone number are now being used for iMessage and FaceTime on a new iPhone”.

Both times I’ve checked my devices list and seen no new devices, and have also not received any security emails from Apple. I also have 2FA turned on. The device names for the new logins match up too, albeit it’s just “iPhone”. I’ve changed my password just to be extra careful.

I’m also not sure if it is relevant, but my iPhone is only occasionally connected to WIFI, and when it is it is only for a very brief time. Idk if that may affect my phone connecting to the Apple servers, however the times when I get the notifications don’t really line up to when I have connected to WIFI.

So my question is, does anyone know what is causing this and should I be worried? Thanks in advance.