an update:
blank screensaver also causes problem
i am locking the screen manually.
and i can confirm with 50/60 times that i've experienced the problem while
using keyboard input
no problem while using mouse input to get back to normal screen
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Computer hangs after switch user
Well, I'm sorry...
but i think it needs to be opened again
I am facing the same problem again.
though it occurs only when i give a keyboard input to get back to desktop
moving the mouse to get back to desktop works well
and when the keyboard works it takes a little longer (may be not
