When I CTRL-drag any value in the character panel (kearning, leading, etc...) The text doesn't update until I release the mouse. So there is no live updating.
I'm using the latest iteration of PS.
Is this due to some display setting or something? Or is it a bug or is it just A-duh-be
This is a bug introduced in the latest version of Photoshop CC 2018, update 19.0.1. That is why I reinstalled update 19.0 on my computer. Adobe is aware of the bug.
Just to add to Barbara's correct answer, Adobe have responded to the bug here :