I speak 4 languages, and I have the least exposure to my native language, since I have never lived in the region where it's spoken. My only exposure to it is speaking to my parents, and some TV. I grew up speaking 1 other language as an infant, and 2 more since Kindergarten. I'm quite fluent in these 3 languages, as I have a lot of exposure. (National language, regional language, and English)
Now, I speak my native language very fluently with my parents and a handful of other people. I can start speaking fast and effortlessly off the bat, like with the other 3 languages. But if any other person starts conversing with me in my native tongue, I'm caught off guard. I stammer, fumble a lot for the right words, don't get the pronunciation right, and take help of English a lot. It takes me anywhere between 2 days (if I'm in constant company of that person) and never to start speaking fluently like I do with my parents.
I feel like I'm selectively fluent, like selective mutism, although google doesn't have any results for it. Is this a thing? Is there a proper term for it?
P.S: This handful of people I mention have been around on and off since my childhood. They're uncles and aunts and cousins.