The issue is that the Joy-Cons joystick has what appears to be a design defect that, regardless of how much care is taken, means they have a high likelihood of developing what is known as "drift" or phantom movement without the joystick actually being engaged. This issue has been, at the very least, acknowledged by Nintendo, and for a few years now Nintendo has been repairing/replacing Joy-Cons for free (at least in the US) because of it. I don't know if there have been design changes, but Nintendo's public release response has been mixed in an effort to avoid as much culpability as possible.