Version 4.40 Weird problem with a product in cart. Help to debug needed.

Hello,
I'm having a problem with a product and i want to find what's happening.

When the shoppingcart has this item, the cart page shows it, but cart controller stop working. I can't update the cart, i can't delete the product from the cart and i can't submit the cart.  All the methods of CartController stop working and i get a HTTP ERROR 400 in the browser and the url is "https://localhost:44369/cart". I can't debug because the breackpoints on the methods are never executed.
If i delete the problematic product from the ShoppingCartItem database table, cart controller start to work, properly and all breakpoint start to work.

If i add the problematic product again to the shopping cart (from front end), the problem starts again until i delete it from ShoppingCartItem.

I need help to debug and find the problem with this product.
Any ideas?

Thank you

Look in the System Log to see if any errors

There's a Error 400. Bad request at the system log.

Clear the System Log, so there is no confusion about related messages.
Use F12 to open browser dev tools (in another window).  Go to Console tab.
Add item to cart.  When you see the 400 error, check the console and the system log for errors.
If you need help, Post the full message here.