My Windows 10 have updated to 21H1 and explorer.exe started crushing (and after that it reloads itself). Crushing happens when I click on any active program on taskbar when I want to focus or restore window. I thought that MS update was the problem, but when I did't find any similar problems on net I suspected on StartIsBack. After I uninstalled StartIsBack problem was gone.
So there are some issues between Windows 21H1 and StartIsBack