After upgrading to 20.2, then log in, type the password, and to the desktop, but the under taskbar disappear, and wait for few seconds, the log in pw bounce out again, and type again the pw log in, same as previous desktop without taskbar under. Then few seconds bounce out the login pw windows. Then infinite loop and can't use the OS now. Tried crtl+F2 to tty mode, and update, dist upgrade, upgrade, etc. but none of them works. finally I just downloaded the 20.2 iso and reinstall the whole system.