In my game for some odd reason the slider to select quantity is not working I use MWSE with a few of Fliggy's mods I wonder if there the case? it is getting to be real annoying :brokencomputer: and I hope someone has the solution to help me out I hope.

If you mean the quantity selection window does not appear, are you using the latest MCP beta? One of its added features swaps item stack behavior to 'take all' by default, where as you then need to shift-click the stack to open that window.