ESC brings up Pause Menu, but cannot get it to 'dismiss' it.

There are 2 ways (maybe more):

Either you set the “UIMode” to “Game and UI” and make sure to set a bool or something in your Character that blocks his Input.

OR

You set the “UIMode” to “UIOnly” and override the “OnKeyDown” (or similar name) Function of the Widget you are using and tell it
to listen for the ESC key. Then, instead of the PlayerPawn, the Widget takes care of reenabling the GameInput.