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ISM/HISM Lightmap error in level streaming

Hi, I am not good at English. I would appreciate your understanding. :)

I am experiencing Instanced Static Mesh (ISM) / Hierarchical Instanced Static Mesh (HISM) lightmap errors in level streaming and lighting scenarios.

Please see the screenshot below.

alt text

alt text

In order to reproduce this:

  1. Set "Project Settings - Streaming - UseBackgroundLevelStreaming = false"

  2. Prepare BP with ISM or HISM.

  3. After you create a sublevel, you configure the sublevels to stream through the streaming volume.

  4. Place ISM / HISM BPs at each sublevel.

  5. Create a lighting scenario level.

  6. This lighting scenario level is configured to be loaded during playtime using a trigger or the like.

  7. After execution, load the lighting scenario level through the trigger and load / unload the sublevel.

  8. You can confirm that the ISM / HISM light map is faulty.


  1. It can be prominently displayed in dark environments where Directional Light does not reach. (Environment with a roof)

  2. The more objects placed in the level (large texture size), the more lag happens during streaming load / unload, and I had to set UseBackgroundLevelStreaming = false in my project.

  3. Only ISM / HISM has been confirmed to be a problem, and there is no problem with BP made from static mash or static mash components.

  4. Simple sublevel streaming without a lighting scenario is not reproducible.

  5. This is also reproducible in 4.19 Preview 4.

The test project download link is: https://drive.google.com/file/d/1vZdSeXSST00eZL9FHmjgeRO-J5D5avEu/view?usp=sharing

Thank you for reading my difficult English.

Product Version: UE 4.18
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asked Feb 23 '18 at 04:07 AM in Rendering

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avatar image Hyunwoo Kang Feb 23 '18 at 04:15 AM

i have same issue. 4.18.3 and 4.19 preview

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