Been debugging this problem in our project, and it is definitely something with masked/translucent materials. We have an runtime gizmo used in our project to select actors and after a few selections, the project always crashes. The runtime gizmo has masked/translucent materials. As soon as I disabled the gizmo, the problem was gone for 15-20 minutes, but eventually it has crashed still in a scene with some translucency/masked materials. It might be a good starting point for the debugging.