4.9P3 lightmass crash

Development Rendering
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1

I just tried out the latest 4.9 preview, number 3 and I’m getting a crash in lightmass when I go to build the lighting that I never got before. It doesn’t actually crash the editor, but it never is able to build.

It goes like this:

=== Lightmass crashed: ===
Assertion failed: (Index >= 0) & (Index < ArrayNum) [File:D:\BuildFarm\buildmachine_++depot+UE4-Releases+4.9\Engine\Source\Runtime\Core\Public\Containers\Array.h] [Line: 678]
Array Index out of bounds: 27491 from an array of size 27491

53762-lightmass_crash.jpg
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2

Hi Eric,

I have recently setup a troubleshooting guide for Swarm Agent/Lightmass for these types of errors over on our Wiki here: A new, community-hosted Unreal Engine Wiki - Announcements - Epic Developer Community Forums

While this error is not specifically up there yet some of the more basic troubleshooting steps may work to help resolve this for you.

  • Try Cleaning and Validating your cache.
  • Delete the cache folder
  • testing if this is happening in a blank scene or project vs your current project.
  • reimporting your assets in case any are corrupted in some way. (I’ve seen a user post that this resolved the issue, but I’m not sure if that is actually the case as they resolved the issue before I had responded.)

Give these a shot and possibly some of the other general suggestions on the Wiki page and let me know if that ends up resolving the issue. I’d like to add this to the guide, but I’ve never had a solid repro case to make it happen and haven’t had to resolve it myself unfortunately.

Thanks!

Tim

3

Well, that was simple - I just needed the first step you mentioned, Clean and Validate cache.

That did the trick.

thanks Tim!

4

Thanks for letting me know and I’m glad everything is working now! :slight_smile:

5

Thanks, this #1 was exactly my problem too! Great community here.

6

Since this seems have resolved the issue for two people I’ve gone ahead and added that to the Swarm Troubleshooting Wiki now. Thanks! :slight_smile: