Dedicated Server crashes when client connects in particular circumstances

Running a dedicated server with the setup in this fairly simply project causes a crash when a client connects. I'm unaware of the actual cause but getting the reproduction was all I could do.

Logs attached from the crash.

Regression?: YES
This did not happen in 4.11.2 (CL#2946394)
Earliest known occurrence is 4.12 release (CL#2992821)

Note: This reproduction requires a source built engine

1. Download the attached project and generate project files, build it for Development Editor / Win 64 and then open the project
2. Package the project for Development
3. Close the project and then rebuild the project for Development Server / Win64
4. Once the compilation completes, take the BugServer.exe from Binaries/Win64 and copy it to the packaged project's Binaries/Win64 folder.
5. Launch BugServer with the following parameter:
   -log
6. Launch Bug with the following parameter:
   127.0.0.1
   Result: BugServer crashes once Bug connects to the server.
   Expected: BugServer should not crash in this scenario.