cannot customize themes

[Ilane]

Basic details:
Country: Israel
Device: Redmi Note 4X
Android version: 6.0 MRA58K
MIUI: Global 10.2.1.0 MBFMIXM

So, does this forum deal with Global MIUI?
If affirmative, I need help:

I have recently upgraded my device to MIUI 10.
I cannot customize Themes.

I reach the screen "Customize theme". Then I select one of the 6 options, for example "Dial pad", and get to the next screen, "Dial pad" but it always goes back after 1 second to the "Customize theme" screen. It doesn't matter if I click an option during that 1 second I am on the "Dial pad" screen. Same for the other 5 options on the Customize theme screen, which are set at Default, and I cannot customize.

Thanks.