I ran into the same problem, that suddenly the Level Blueprint created, although I used a DoOnce Node, 2 Widgets at the same time. When I printed the Display Name of the Level Blueprint to Screen, it showed “MyLevel1” and “MyLevel5”.
The Bug occured randomly when I was working on the Level Blueprint. The only things I recognized before were that when I pressed “create new Variable” an unrecognized “MyBlueprint” Tab occured and “Save All” showed some Blueprints I did not edit.
Engine Version: 4.18.3