When opening a project while another project is already open UE4 now force closes that other instance first without even saving! Pre 4.11 I often opened multiple projects to get content and blueprint code from one project to the other which is now hardly possible. Content would work but is annoying and copy paste blueprint from on project to the other will not because UE4 will overwrite the copy paste cache with junk in the close project and open project process. I would call it a bug because I can’t see the feature in this, maybe it even crashes the other instances? I’m using Win7 64Bit and I usually have SteamVR running if that matters.
Edit: This even happens when selecting standalone game in the play settings, so it closes the editor when playing a standalone game!