Are you setting the visibility in the UMG graph? I’ve experienced some issues receiving input within that blueprint. I would recommend an external approach. The way I usually drive changes in UMG (such as changing the color, or hiding elements like you are) is by casting to the widget. You can do this by using “Create Widget” in a separate blueprint (I manage mine in my Game Mode BP), selecting your UMG blueprint under “Widget Type”, and dragging off the return value to create a cast to the widget. You can then drag off the "As _____(name of your UMG widget) node on the cast to grab your different buttons and things from UMG and edit them by using a Get and changing their parameters (as long as they are set as variables). This approach is demonstrated here:
https://docs.unrealengine.com/latest/images/Engine/UMG/QuickStart/4/New_25.jpg
GameHUD being their widget blueprint.