I think your problems is due to something related to get player controller, basicly at some point you forget to redirect the control back to your character, Im not an expert but I’ve done some tests with widgets menus so let me search in my projects and I will try to help you with some captures:
EDIT 1: Try this:
at the main menu blueprint create an start button event and then link that to the functions that makes exit the menu and return player controllers just like this:
green one says: get player controller (sorry its in spanish)