Personally I have been battling with this for a couple of days and even reinstalled my whole system in order to verify it. There is a bug regarding the sound engine of UE4 which crashes the editor and Game(s) that are supported by UE4 Engine. Also I have made a topic regarding the game located here which contains the details as well.
If you look into the log, this does not seem to be related to 7.1 at all… Something (a network error?) causes the engine to exit prematurely, and it crashes while deinitializing the PhysX (which is arguably a different problem):
[2015.03.07-17.03.07:346][768]LogNetTraffic:Warning: Received unreliable bunch before open (Channel 59 Current Sequence 0)
[2015.03.07-17.03.07:347][768]LogNetTraffic:Warning: Received unreliable bunch before open (Channel 59 Current Sequence 0)
[2015.03.07-17.03.07:388][769]LogNetTraffic:Warning: High single frame packet loss: 50
[2015.03.07-17.03.12:001][771]LogNetTraffic:Warning: High single frame packet loss: 32
[2015.03.07-17.03.17:632][815]UT: OnPresenceUpdated Successful
[2015.03.07-17.03.24:545][913]Closing by request
[2015.03.07-17.03.24:545][913]LogGenericPlatformMisc: FPlatformMisc::RequestExit(0)
[2015.03.07-17.03.24:662][914]LogExit: GameNetDriver IpNetDriver_251 shut down
[2015.03.07-17.03.24:789][914]LogExit: Preparing to exit.
[2015.03.07-17.03.25:006][914]LogExit: Game engine shut down
[2015.03.07-17.03.25:081][914]LogParticles: Destroying 0 GPU particle simulations for FXSystem 0x0x2c63f320
[2015.03.07-17.03.25:081][914]LogExit: Object subsystem successfully closed.
[2015.03.07-17.03.25:209][914]LogLinux: === Critical error: ===
Unhandled Exception: SIGSEGV: invalid attempt to access memory at address 0x00000065
[2015.03.07-17.03.25:210][914]LogLinux: Fatal error!
[Callstack] 02 0x00007f7dc0783353 ReportCrash(FLinuxCrashContext const&)
[Callstack] 03 0x0000000000421960 EngineCrashHandler(FGenericCrashContext const&)
[Callstack] 04 0x00007f7dc07854d0 PlatformCrashHandler(int, siginfo*, void*)
[Callstack] 05 0x00007f7dc0fcb8d0 /lib/x86_64-linux-gnu/libpthread.so.0(+0xf8d0) [0x7f7dc0fcb8d0]
[Callstack] 06 0x00007f7dbf098494 physx::NpFactory::release()
[Callstack] 07 0x00007f7dbf098720 physx::NpFactory::destroyInstance()
[Callstack] 08 0x00007f7dbf061eb3 physx::NpPhysics::release()
[Callstack] 09 0x00007f7dbeac62f9 TermGamePhys()
[Callstack] 10 0x0000000000419bc0 FEngineLoop::Exit()
[Callstack] 11 0x000000000041a3a4 GuardedMain(wchar_t const*)
[Callstack] 12 0x0000000000422118 ./UE4(main+0x758) [0x422118]
[Callstack] 13 0x00007f7db9563b45 /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf5) [0x7f7db9563b45]
[Callstack] 14 0x000000000040fb36 ./UE4() [0x40fb36]
Tried to mess around with a Mac OSX on a Mac Pro (Late 2014) and it has identical crash and output when running 5.1 or 7.1 surround. Compared the outputs trough command line and the output was identical.