Possible bug.
Once the text of a button is created it cannot be changed.
var button = BABYLON.GUI.Button.CreateSimpleButton(“showHistory_button”, “I refuse to change” );
So, button.text = “blah blah” will not change the original text of the button from “I resuse to change to” blah blah".
Here is a demo and a workaround using a button caption.
https://www.babylonjs-playground.com/#X2DCJS#1