To reproduce:
1. Open the scene and notice that there's a CanvasGroup component attached to the GameObject named "Panel" with an alpha value of 0.5.
2. Use the Inspector to disable the GameObject named "Panel"
3. Re-enable the GameObject
4. The panel won't be rendered with 0.5 alpha anymore
5. If you check in the Inspector you'll notice that the alpha value of the CanvasGroup that's attached to the "Panel" object suddenly has a value of 1, but it should be 0.5 (might have to click into the field to force the Inspector to redraw).