Problem is network related, been getting a lot of it too recently, item server drops connection and you cant move anything.. slow responses also become a pain because there is a delay before something moves. Just try to move 1 thing, if it doesn't move quit and restart TF2 once often solves the server connection

yep, it won't. But if/when the items aren't shifting, those keyboard shortcuts make sorting your bp much faster.

using page up and down isn't going to solve the items from shifting and disappearing and stacking on top of each other. it's a pain in the ass shifting inventory.

Some custom huds also allow you to use A and D aswell

Fun fact, you can use Page Up/Down to navigate pages in your inventory.