So I made a menu system (vers. 4.4) and it works but only when in the ‘Main Menu’ level. I have a ‘Main Menu’, a ‘Pause Screen’, and an ‘Exit Screen’. When I click ‘Exit’ from the ‘Main Menu’ level I get my ‘Exit’ screen. If I click ‘New Game’ I get my first level (with pretty much everything I wanted there as far as my HUD goes) but the Main Menu screen is still there and I can’t get it to go away. I haven’t been able to get the ‘Pause Screen’ to work either. I’ve tried every method I can find and it just will not work. I’ve used ‘remove from viewport’, I’ve set the main menu widget value to null, everything (not all at once mind you). So has anyone else had this problem? Does anyone have any ideas on how to remedy this.
Check out my post here: https://forums.unrealengine.com/showthread.php?49442-UMG-in-4-5-Recommended-workflow-(and-can-t-cast-to-widget)
UMG changed when it came out of experimental mode (4.4), I’d recommend upgrading as your project. As my post is yet to be answered take it with a pinch of salt but I’ve read up a bit on it and have it working the way I describe it in my post. I found 4.4 a bit buggy (as expected) anyway - text input not saving and a serious load of crashes. 
Good luck!