UE5.7 Regression: UMG Background Blur with Corner Radius becomes invisible in packaged builds (UE5.6 OK)

Development Getting Started & Setup
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Engine Version(s): UE 5.6.x (works), UE 5.7.x (broken)
Platform: Windows (packaged build)
Repro Rate: 100% (for me)

Summary

In UE 5.7, the UMG Background Blur widget renders correctly in PIE/editor, but in packaged builds it becomes fully transparent / invisible when Corner Radius > 0. This appears to be a regression compared to UE 5.6, where the same setup works in packaged builds.

Steps to Reproduce (clean project)

  1. Create a new Blank project (Blueprint), no starter content.

  2. Create a Widget Blueprint, e.g. WBP_TestBlur.

  3. In the widget: Canvas Panel → SizeBox (set a fixed size, e.g. 600x400).

  4. Add a Background Blur widget inside the SizeBox.

  5. Set:

    • Blur Strength = 20

    • Corner Radius = 20 (any non-zero value repros)

  6. In Level Blueprint (BeginPlay): Create Widget → Add to Viewport.

  7. PIE/editor: blur shows correctly with rounded corners.

  8. Package for Windows (Development or Shipping) and run the packaged executable.

Actual Result

  • UE 5.7 packaged: Background Blur is not rendered (transparent/invisible) when Corner Radius > 0.

  • If Corner Radius = 0, Background Blur renders again (but without rounded corners).

Expected Result

Background Blur should render in packaged builds with Corner Radius enabled, consistent with PIE/editor and UE 5.6 packaged behavior.

Notes / Regression

  • UE 5.6 packaged: works correctly with Corner Radius enabled.

  • UE 5.7 packaged: broken as described above.

  • Workaround: set Corner Radius to 0 (loses rounded corners).