Topic: B button not working SMB

My son has a Nintendo switch and while playing super Mario bros U the b button stops working. If we turn off the switch and turn it back on it works again for a while. Is there something that causes this or is something wrong with the switch? Thanks

That sounds like a problem with the controller.
Can you specify what kind of Nintendo Switch or game controller you have?

The standard Nintendo Switch model has a pair of detachable controllers called Joy-Cons.
Whereas the Nintendo Switch Lite model does not have detachable controllers.
Separate to the Switch system or the Joy-Con controllers, there are are all sorts of official and unofficial controllers.

Is your son playing the Mario game using the Nintendo Switch as a handheld, or on a TV set?

On the Switch's home menu, you can go into the System Settings and find a Test Input Devices option under Controllers and Sensors.
https://en-americas-support.nintendo.com/app/answers/detail/a...
You may be able to use this to test the B button on the controller you are having issues with.
If you are using an official controller or system provided by Nintendo, it may be eligible for repair or replacement under Nintendo's warranty.
https://en-americas-support.nintendo.com/app/products/detail/...

It’s happened in hand held mode and playing on the tv using nano controllers. I’ve exited out of the game while playing on the tv and the b button works fine. I’ve also restarted the switch and went back into super Mario and the b button will work fine for a while. I just don’t know if it can be an issue with the game or the system since it happens with the joy cons and the separate controllers.
Thanks

This sounds like a problem with the right Joy-Con controller, or nano controller you call it.
Does the problem with the B button happen in any other games, or is it only this Mario game?
The B button is used for jumping in this game, and depending on what is happening in the game, it might not be possible to jump. It might be the case that the button is working, but the game is not letting you jump for another reason?

How would you describe the problem, is it that the button is not responsive, or that the game is not reacting the way you expect it to?
The A button has the same function during gameplay, allowing Mario to jump.

The b button does nothing when it’s not working correctly. We have 2 nano controllers and the b button won’t jump on either controller but still will with the a button. Same for if we’re playing in hand held with the joy con. That’s why I thought it has to be the system or the game. I don’t know if something can go wrong with the game cartridges though.

Oh, by Nano controller do you mean these?
https://www.powera.com/product/nano-enhanced-wireless-control...
These are third party controllers, I thought you were giving the Joy-Cons your own name for being small controllers.

If you have multiple controllers experiencing this issue, I have to wonder if you have accidentally changed the button controls in game.
The default control scheme uses the X and Y buttons to run, and the A and B buttons to jump.
But when you pause the game, a button on the bottom right will show which control scheme you are currently using. It can be changed so that the B and Y buttons run, and the A and X buttons jump.