Fatal Error
There is definitely something wierd going on there when the engine attempts to read or serialize content from the pak file. At the assertion break the WaitEvent / Trigger event reference/value is null, as well as almost all variables in that section.
if (WaitEvent)
{
WaitEvent->Trigger();
}
Resulting in crash: EXCEPTION_ACCESS_VIOLATION reading address 0xffffffff
Let us know if you figure anything out, this has been shipping breaking for weeks now. 
The breakpoint can vary when it crashes:
Game.exe!FSafeRecyclableEvent::Trigger() [h:\unrealengine-release\engine\source\runtime\core\private\misc\eventpool.h:50]
Game.exe!FPakProcessedReadRequest::RequestIsComplete() [h:\unrealengine-release\engine\source\runtime\pakfile\private\iplatformfilepak.cpp:2740]
Game.exe!FPakAsyncReadFileHandle:: DoProcessing() [h:\unrealengine-release\engine\source\runtime\pakfile\private\iplatformfilepak.cpp:3079]
Game.exe!TGraphTask<FAsyncIOCPUWorkTask>::ExecuteTask() [h:\unrealengine-release\engine\source\runtime\core\public\async askgraphinterfaces.h:886]
Game.exe!FTaskThreadAnyThread::ProcessTasks() [h:\unrealengine-release\engine\source\runtime\core\private\async askgraph.cpp:1277]
Game.exe!FTaskThreadAnyThread::ProcessTasksUntilQuit() [h:\unrealengine-release\engine\source\runtime\core\private\async askgraph.cpp:1171]
Game.exe!FTaskThreadBase::Run() [h:\unrealengine-release\engine\source\runtime\core\private\async askgraph.cpp:643]
Game.exe!FRunnableThreadWin::Run() [h:\unrealengine-release\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:76]
Game.exe!FRunnableThreadWin::GuardedRun() [h:\unrealengine-release\engine\source\runtime\core\private\windows\windowsrunnablethread.cpp:33]