Just adding this in case it helps others. I wanted to select a specific item via script and while searching other topics lead me to use the following line when I pause my game, it would only work the first pause.
EventSystem.current.SetSelectedGameObject(PauseCanvasReloadCheckpointGO, null);
The solution was to null it out on unpause.
EventSystem.current.SetSelectedGameObject(null, null);
Now it correctly selects the pause menu Reload Checkpoint button every time the pause menu is brought up.