Hello, what do you mean? If you switch to the Storefront theme, do you have the same problem? If yes, it is an issue with WooCommerce and you will need to contact them.
Try rewrite quantity in the cart.
I mean in the cart you try rewrite quantity of one product if you have more product in the cart.
Process:
1. you give 2 products at least to cart
2. go to cart
3. click to quantity number of one product and delete number (I think delete number 1)
4. write “50” for example
writed number 50 will be changed in all product (in all cart′s rows).