Hello,
I had the same problem for a while, but when I made the menu smaller, I saw the level was already open. I only followed the [UE4 documentation][1].
The problem: I hit ‘Play’, the level opens, and in the ‘Level Blueprint’, the ‘Event BeginPlay’ creates the menu widget. On the menu, I hit Play, the ‘Open level’ starts the level again, which creates the menu again.
Solution: Make another level only for the menu, which opens the original playing level.
Easier solution: Don’t use ‘Open level’.
I’m sure others know better solutions, but if someone else has this problem too and can’t find any answer, maybe my solution helps…
[1]: