Editor freezes randomly


We are having an issue where the editor will randomly freeze. In my machine it happens everytime I hit the Play button, however it’s a bit random when the freeze will actually happen. Sometimes is instantaneous, sometimes it takes a few seconds. One of our coworkers is having this issue even just by using the editor but not actually playing.

This started happening after getting the version 4.2 of the engine.

It looks like the engine gets stuck waiting for a thread (see callstack below).

Any idea of what might be going on here?

Here’s the callstack taken from a Debug Editor configuration:

UE4Editor-Core-Win64-Debug.dll!FEventWin::Wait(unsigned int WaitTime) Line 920 C++
UE4Editor-RenderCore-Win64-Debug.dll!GameThreadWaitForTask(const TRefCountPtr & Task, bool bEmptyGameThreadTasks) Line 687 C++
UE4Editor-RenderCore-Win64-Debug.dll!FRenderCommandFence::Wait(bool bProcessGameThreadTasks) Line 715 C++
UE4Editor-Engine-Win64-Debug.dll!FFrameEndSync::Sync(bool bAllowOneFrameThreadLag) Line 6651 C++
UE4Editor-Win64-Debug.exe!FEngineLoop::Tick() Line 2162 C++
UE4Editor-Win64-Debug.exe!EngineTick() Line 53 C++
UE4Editor-Win64-Debug.exe!GuardedMain(const wchar_t * CmdLine, HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, int nCmdShow) Line 135 C++
UE4Editor-Win64-Debug.exe!WinMain(HINSTANCE__ * hInInstance, HINSTANCE__ * hPrevInstance, char * __formal, int nCmdShow) Line 196 C++

Hi cfernandez,

Is this happening on a custom project you are making or can you reproduce it in a new level or project?

Also, could you post your dxdiag, along with your crash logs and dmp files from both you and your coworker?

Below is a link on how to find all of this if you have any questions.

Hi TJ Ballard,

I tried reproducing this issue in a new project from the template but I didn’t get it. It only seems to happen in our custom project.

Here’s the rest of the information:

Branch: We are using a branched version of the UE4 engine source from Github.

Build version: 4.2.0-0+UE4

System Specs:

  • OS: Windows 8.1 64 Bit
  • CPU: Intel i5-4440 @ 3.10GHz
  • RAM: 16GB
  • GFX: NVIDIA GeForce GTX 760
  • DXDIAG: Please note I’ve attached my DXDIAG below.

Log and Dump files:

Hey CFernandez,

It does seem that your issue is with Coherent UI. I can only recommend that you bring this issue up on their forums. Not a lot we can do about their source.



Thanks for the quick answer. By the way, can you please explain me please how did you determine this issue is caused by CoherentUI? I can see the logs have CoherentUI outputs but I don’t see how that means the issue would be caused by CoherentUI.

Hey CFernandez,

It could well be a cooincidence, but alot of the evidence is pointing that way. The fact that the game thread is waiting on the render thread, and the last thing in your log is alot of CoherentUI task spam, it seems like this is related.

Also, the fact that it only happens in your project is suspicious.

I did also come across this on their forums:

Like I said, these could all be a coincidence, but I cannot reproduce this myself.
Have you followed this:

I’d be interested to see your colleagues logs, his issue sounds different from yours.