In some cases, there are missing updates when setting opacity (!= 0.0) to an item that had previously opaciy 0.0.
This is due to the internal data structure, paintedViewBoundingRects, being set to (-1,-1,-1,-1), which means outside the viewport, when the item has opacity 0.0.
Afterwards when you want to show the respective item by updating its opacity, the update is lost.

Test case attached.