DPI Scale Rule set to custom can cause performance issues during design time

When setting the DPI Scale Rule to custom and using a named slot the frame rate of the editor will drop while zooming in and out of a widget that uses the widget containing the named slot.

1. Download the attached project
2. Open the attached project
3. Open the project settings
4. Navigate to the DPI Scale Rule (project settings > User Interface > DPI Scale Rule)
5. Set the DPI scale rule to "Custom"
6. Press the '~' key and input the command "Stat FPS"
7. Open the widget "FPSDrop"
8. Separate the Window for the widget from the main editor (so that you can see the current frame rate as well as the widget designer tab)
9. Click on "NamedSlot_59 (CanvasPanel_1)" in the widget hierarchy
10. Zoom in and out of the designer tab (using the scroll wheel)

Result: The FPS will continue to drop as the zoom is adjusted
Expected: The Frame rate would remain relatively steady.