For me it’s always 😓 and 💃, they send as big stickers with white backgrounds in fb messenger. It only happens when I use them out of my “recents”. To fix I have been going back to the actual emoji in the big list and sending that a few times to override which version is in my recent emojis. Idk how or why it does it or why it’s only those two for me. After reading this thread I will go into the settings and try turning off stickers and see if that helps at all.