Hi,

I tried several methods without success. If you have a Mi Box 3 and you don't care about if you lose your installed apps or some files in the memory, do this:

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Unplug the box.

Press and hold the big button (center button) and the back key AT THE SAME TIME

Now plug your box while you are pressing the buttons.

You are going to see the recovery mode after some seconds.

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Select Wipe Data/factory reset.

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This should fix your problem and of course, you have to install again all your apps.