Comment 9 for bug 1924689

This bug is not limited to changing the scale from lower to higher and is not limited to shadows displaying garbage. It also occurs:

* when changing the scale from higher to lower
* infrequently when new windows or dialogs are created, particularly snap apps like nautilus or gnome-text-editor or modal dialogs such as e.g. evolution

Other effects in addition to shadows displaying garbage are:

* the window not capturing mouse events correctly, other windows below the garbage window capture the events
* the window not being able to capture focus, i.e. come to the front of other windows

The situation can be 'fixed' by maximizing + unmaximizing the window, users can TAB-select the window if it cannot be reached with the mouse.

(Summary from my duplicate bug report https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/2023209)