According to Nintendo Life, Nintendo are working on a fix for the infamous frame rate drops in several Switch games. It seems to stem from issues with the Wi-Fi driver; some people have reported that turning it off or enabling "Flight mode" solves the problem.
http://www.nintendolife.com/news/201...ropping_frames
https://gbatemp.net/threads/turning-...-games.464512/
http://www.nintendolife.com/news/201...ropping_frames
https://gbatemp.net/threads/turning-...-games.464512/