I haven’t been able to reliably reproduce this in a test case, but it happens daily. And this is not the same issue as my old question which I asked prior to learning about the different “modes” of that button; I have it set to “Minimize all Windows” (not “Peek at Desktop”).
The issue: First I click the bottom-right button to show the desktop (minimize anything that is on the screen). Then I click it again, expecting to get back whatever I was looking at before clicking it. Usually, this does happen.
But sometimes, it does not. Instead of bringing back my Vivaldi that was maximized, for example, it brings up pgAdmin 4 maximized, as well as a Dolphin instance on top of it. Both of those applications were minimized when I first clicked the button, so they should not be involved at all.
Also, if you have two instances of an application opened, so that they group in the taskbar, it can bring up the right application but the wrong instance. (For example, the secondary Vivaldi browser profile instead of the primary one.)
What causes this to happen? It varies seemingly depending on what programs you have opened/maximized/non-minimized when initially clicking the button. It actually eerily reminds me of similar issues while I was using Windows 10.