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

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

Product Version: UE 4.19
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asked Mar 15 '18 at 01:21 PM in Bug Reports

avatar image

lbeim
31 1 3 7

avatar image Jeff A ♦♦ STAFF Mar 15 '18 at 02:30 PM

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

avatar image lbeim Mar 26 '18 at 11:07 AM

Hi, I can't find my bug report here: https://issues.unrealengine.com/issue/search?q=vr&resolution=∁onent=&sort=created

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

Thank you very much.

avatar image lbeim Mar 15 '18 at 03:01 PM

Hi Jeff, I made a report.

Thank you

avatar image Mr Janks Mar 15 '18 at 09:31 PM

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?

avatar image Adapt Mar 19 '18 at 08:27 PM

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.

avatar image Jamesant8 Mar 21 '18 at 02:52 AM

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

avatar image Parth Patel Mar 23 '18 at 10:06 PM

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,

avatar image Ben_Cykyria Mar 28 '18 at 08:56 AM

Maybe this is related: https://answers.unrealengine.com/questions/772248/ue419-vr-crash-when-playing.html#comment-772248-form

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.

avatar image mordentral Mar 28 '18 at 12:47 PM

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.

avatar image Ore Creative Mar 28 '18 at 03:31 PM

Anyway to do this in blueprints?

avatar image mordentral Mar 28 '18 at 06:49 PM

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

avatar image Ore Creative Mar 28 '18 at 07:27 PM

How would I go about "Turning off late updates"?

avatar image mordentral Mar 28 '18 at 07:31 PM

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

avatar image Ore Creative Mar 28 '18 at 07:35 PM

Is it disable low latency update?

avatar image FluxDevs Mar 29 '18 at 10:36 AM

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

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7 answers: sort voted first

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.

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answered Mar 29 '18 at 01:03 PM

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Ore Creative
67 4 8 14

avatar image Constantin Suman Oct 01 '18 at 10:49 AM

In UE4.19 checking "Disable Low Latency Update" WORKED, there are no more crashes.
In UE4.20 the bug is not present any more.
Thanks for a quick-fix solution.
Note: keep in mind (in UE4.19 ) to refactor the functionality which was based on low_latency update.

One more thing: given the fact that many developers fall into problems with the illogical naming of this variable (if true => isDisabled (should be enabled)), I'd refactor the name "Disable Low Latency Update" into "Enable Low Latency Update" defaulting to true.

avatar image mordentral Oct 01 '18 at 12:16 PM

It shouldn't be in 4.20, it was corrected in a late hotfix in 4.19 and 4.20 still has the fix applied.

avatar image Constantin Suman Oct 01 '18 at 12:28 PM

Hi, mordentral. Thanks for your message. I double-checked.
It was my fault. The error is present in 4.19 and not in 4.20. I will update my previous comment. If you will delete your comment, I will delete mine, so not to create confusion and mass-commenting.

avatar image Dover8 Jun 12 '19 at 10:51 AM

I'm still experiencing a crash in 4.21 The bug UE-62486 is also still open

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Hey Guys,

Just wanted to let you all know this should be fixed in 4.19.1

https://issues.unrealengine.com/issue/UE-55445

Thanks,

Alex

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answered Apr 03 '18 at 03:57 PM

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Alex O ♦♦ STAFF
2.6k 4 8 10

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Still crashing with disable low latency update unchecked.

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answered Mar 29 '18 at 11:24 PM

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unrealroly
0 1 1

avatar image mordentral Mar 30 '18 at 03:17 PM

"Checked", he wrote the wrong word, also you would need to make sure it is the same crash.

avatar image unrealroly Mar 31 '18 at 02:47 AM

Thank you mordentral. I was wondering because it was unchecked by default. I haven't had any crash with this temp fix.

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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,

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answered Mar 23 '18 at 10:06 PM

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Parth Patel
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I'm having the same issue. The same Crash Reporter Log.

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answered Mar 24 '18 at 01:33 AM

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unrealroly
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Still crashing with disable low latency update unchecked.

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answered Mar 29 '18 at 11:25 PM

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unrealroly
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Hey, guys! Try to create new scene map and copy all asset or just create new project and migrate all asset to content browser. I solve this issue following this steps.

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answered May 04 '18 at 07:23 AM

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onliner007
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avatar image mordentral May 04 '18 at 12:16 PM

It was fixed in 4.19.1

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