Slide Background Fill issue(Preview and Publish unaffected)

I’m experiencing significant stuttering and lag in the Storyline editor when working on slides that contain multiple shapes converted to “Slide Background Fill.”

This lag only occurs in the authoring environment — both Preview and Published outputs run perfectly smooth, so it doesn’t appear to be a GPU or browser-side issue.

From what I can tell, the performance drop seems to be related to how Storyline’s editor renders multiple baked fills simultaneously, possibly due to redraw load in the WPF interface. (Assuming that Storyline’s authoring environment is WPF-based — which is likely, given it’s a Windows-only desktop application built on the .NET framework — please correct me if I’m wrong.)

I prefer creating the parallax effect this way because it allows me to apply shadows on transparent shapes. Using standard shapes, zeroing transparency or “no fill” doesn’t display shadows correctly — the shadow disappears when the fill is transparent. Converting shapes to slide background fills preserves both the transparency and the shadow rendering, which is essential for achieving realistic parallax depth and lighting.

Steps to reproduce:

1. Create a new Storyline project.
2. Add slide background (Format background > Fill > Picture > Insert image). 
3. Add several large shapes covering parts of the slide.
4. Convert each to “Slide Background Fill.”
5. Navigate slides and notice stuttering in editor navigation.

Expected:
Smooth authoring performance similar to slides using regular shapes.

Actual Result:
Significant stuttering when navigating slides or interacting with the timeline containing multiple background-fill shapes.

Additional Notes:

• Performance is completely normal in both Preview and Published versions.
• This behavior is isolated to the authoring workspace.
• It seems related to the way Storyline handles redraws of slide background fills inside the WPF-based editor.

If this is a recognized limitation of the authoring environment, I’d appreciate any suggested workarounds or optimization practices to maintain smooth navigation while keeping the same visual results.

File attached to help reproduce faster.