Select your fighter with the controller you are using.

Okay, so SW might not be the ideal place to post about this issue, but I don’t want to have to go through the trouble of having to set up an account on a video game website. When I’m playing SSBU every so often I get interrupted with a screen that demands that I select my fighter with the controller I’m using. About two out of three times this happens I just press L and R, select my character, and move on, no big deal; however, about one out of three times pressing L and R does nothing, which leaves me stuck and unable to resume playing. I’ve tried turning the Switch off and back on again, but when I turn it back on the only buttons that work are the buttons that take me straight back to the same screen on SSBU I was stuck on before I turned the Switch off (it won’t let me change my software or player or read news stories or anything). The only way out of this I’ve found is to take my controller apart and just use half the controller so I can select my fighter, which I really don’t like because it means having to play using only half my controller, and it makes it impossible to get out of SSBU and return to the Switch’s home screen (because the home button is on the other half of the controller, the half I can’t use), and it’s always been a major pain in the ass to try to get the Switch to start recognizing the other half of the controller again once I‘ve resumed playing with just the one half. What’s wrong with my game or my Switch? How can I get out of this current predicament? And how can I avoid this situation in the future?