UE4 Editor crashes after displaying a “Fatal Error!” message box, and then when you try to reopen the project throughout UE4 Launcher, it keeps showing the same message box and be silent.
Go to your project_folder/Saved/Logs/ and open project_name.log with a text editor. You should be able to see where it failed to load the project. In my case, I was referencing my game mode in a subclass of UActorComponent. I realized that when editing mode is executed (which is the default mode when you launch your project in editor,) its constructor gets called, but GameMode is not valid at the moment. I simply moved the part to BeginPlay method and it worked.