Could be an issue with your Switch, and not the game. Does the button work properly out of the Witcher? If so, it could be a bug with the game. Have you attempted loading an earlier game, charging your remote (if it's out of battery), and rebooting? Hope you get it sorted!
Good suggestion. Though it may be more worthwhile to send it to Saber Interactive rather than CDPR, since Saber did the port. Though unfortunately, I can't seem to locate a contact email for Saber. Could've sworn I saw someone post a screenshot of one few weeks ago though. Regardless, sending it to CDPR Support should still work fine.