Constant crash in VR Preview with VR Template Assertion failed !IsUnreachable

Development Programming & Scripting Blueprint
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1

Hello,
with the UE 4.19 VR Template I get constant crashes when previewing the Level “MotionControllerMap” in VR (“VR Preview”)
It is a new project, created with the launcher. I’m using the HTC Vive.
It does not crash if the motion controllers are turned off.
As soon as I turn on one controller the problem occurs.

If you need additional information please let me know.

This is the Crash Reporter Log:

Assertion failed: !IsUnreachable() [File:D:\Build++UE4+Release-4.19+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\ScriptCore.cpp] [Line: 1189] MotionControllerComponent /Game/Maps/UEDPIE_0_Memory_Master_Level.Memory_Master_Level:PersistentLevel.BP_MotionController_C_1.MotionController Function: ‘/Script/HeadMountedDisplay.MotionControllerComponent:OnMotionControllerUpdated’

UE4Editor_Core!FDebug::AssertFailed() [d:\build++ue4+release-4.19+compile\sync\engine\source\runtime\core\private\misc\assertionmacros.cpp:419]
UE4Editor_CoreUObject!UObject::ProcessEvent() [d:\build++ue4+release-4.19+compile\sync\engine\source\runtime\coreuobject\private\uobject\scriptcore.cpp:1189]
UE4Editor_HeadMountedDisplay!UMotionControllerComponent::PollControllerState() [d:\build++ue4+release-4.19+compile\sync\engine\source\runtime\headmounteddisplay\private\motioncontrollercomponent.cpp:453]
UE4Editor_HeadMountedDisplay!UMotionControllerComponent::FViewExtension::PreRenderViewFamily_RenderThread() [d:\build++ue4+release-4.19+compile\sync\engine\source\runtime\headmounteddisplay\private\motioncontrollercomponent.cpp:516]
UE4Editor_Renderer!ViewExtensionPreRender_RenderThread() [d:\build++ue4+release-4.19+compile\sync\engine\source\runtime\renderer\private\scenerendering.cpp:2680]
UE4Editor_Renderer!TGraphTask

2

Hello,

We’ve recently made a switch to a new bug reporting method using a more structured form. Please visit the link below for more details and report the issue using the new Bug Submission Form. Feel free to continue to use this thread for community discussion around the issue.

https://forums.unrealengine.com/unreal-engine/announcements-and-releases/1410408-unreal-engine-bug-submission-form

Thanks

3

Hi Jeff,
I made a report.

Thank you

4

Having the exact same issue. Anyway to make it stop? How can we follow these bug reports if there isn’t a public forum option anymore?

5

Exact same problem here. I think it happens when one of the motion controllers loses tracking even if it’s for a micro second. And it happens in a completely clean project as well.

6

same problem here too, only crash when controller turned on.

7

We are having same issue. Sometimes it happens instantly and sometime it happens after some time. Is this a bug or sometime on our end. Here is log report

Assertion failed: !IsUnreachable() [File:D:\Build++UE4+Release-4.19+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\ScriptCore.cpp] [Line: 1189]
MotionControllerComponent /Game/Maps/UEDPIE_0_MASTER.MASTER:PersistentLevel.BP_MotionController_C_1.MotionController Function: ‘/Script/HeadMountedDisplay.MotionControllerComponent:OnMotionControllerUpdated’

THanks,

8

We are having same issue. Sometimes it happens instantly and sometime it happens after some time. Is this a bug or sometime on our end. Here is log report

Assertion failed: !IsUnreachable() [File:D:\Build++UE4+Release-4.19+Compile\Sync\Engine\Source\Runtime\CoreUObject\Private\UObject\ScriptCore.cpp] [Line: 1189]
MotionControllerComponent /Game/Maps/UEDPIE_0_MASTER.MASTER:PersistentLevel.BP_MotionController_C_1.MotionController Function: ‘/Script/HeadMountedDisplay.MotionControllerComponent:OnMotionControllerUpdated’

THanks,

9

I’m having the same issue. The same Crash Reporter Log.

10

Hi,
I can’t find my bug report here: Unreal Engine Issues and Bug Tracker (Search Results)

Files I provided were downloaded but I got no feedback.
Can you maybe give an update here?

Thank you very much.

11

Maybe this is related: UE4.19 VR crash when playing - XR Development - Unreal Engine Forums

Happens with a unmodified, newly created VR Template project. Can you please check this? Create a new project with VR Template, then go to motioncontrollermap, VR Preview, and play around for a few minutes. Crash occurs within 2-5 minutes. SteamVR release, SteamVR beta, newest NVidia Drivers.

12

This is caused from the render thread trying to call a blueprint event that was added in 4.19.

I filtered it behind IsInGameThread in my personal code for the time being, however since polling the location is only really done in the motioncontroller tick for the game thread it would be valid to just move the event into there instead.

13

Anyway to do this in blueprints?

14

Turning off late updates on the controller should skip the scene view processing and avoid the bug.

Will let you test stuff until it is fixed.

Otherwise, no

15

There is a boolean on the motion controllers details panel, DisableLateUpdates.

16

How would I go about “Turning off late updates”?

17

Is it disable low latency update?

18

I hope Epic Games is looking into this cause a lot of people have this bug

19

Temporary fix: in the details panel of the motion controller blueprint check disable low latency update. Your crashing will stop. (Thanks mordentral)

Edit: I’ve been working in for hours with not a single crash after enabling low latency update. Make sure you save and restart the editor if you are still having crashes.

20

Still crashing with disable low latency update unchecked.