Description

Starting with Unreal Engine 5.4, the logic for adding ISM instances by adding ISM components in the Construction Script (like below) has failed. 

[Image Removed]

This issue accidentally was introduced at CL28594968. From this change, UInstancedStaticMeshComponent::CreateSceneProxy() started to early-return with null in the above repro scenario, due to a new flag bInsInstanceDataApplyCompleted.

Steps to Reproduce
  1. Download the repro project, ISMIssue54.zip, and unzip it.
  2. Open the project.
  3. Open ConstSrcTest from the content browser.
  4. Click BP_ConstTest from Outliner.
  5. Change Default > Static Mesh in the Details panel.
  6. Confirm the displaying mesh disappers.

Expected Behavior: The mesh chosen at step 5 appears (technically as an ISM instance)

Workaround in this repro project: Turn off and on Default > Generate flag to run ConstructionScript again.

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Fixed
ComponentUE - Graphics Features
Affects Versions5.4
Target Fix5.5
Fix Commit35017787
CreatedJul 21, 2024
ResolvedJul 23, 2024
UpdatedJul 30, 2024
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