I am from the States and went to Columbia for a couple of weeks last year. I had to reset my phone while there. I’ve been back in the US for over a year. Periodically ever since, my iPhone messages app has, when someone in the US texts me, instead of putting me back into the existing conversation, has created a new conversation with them, myself, and myself with a +1(xxx)xxx-xxxx version of my phone number. When I reply, my friend gets a reply, but I do too as a recipient. I formatted my phone last year and it stopped, but then I just got a text from a friend who I hadn’t texted with since before my trip, and it did the same thing. iPhone SE 2020; 16.6.1, though this has been through several era software updates. Thanks!