X1 Yoga auto backlit gone?

[Wall]

Hi all,
a few days ago, presumably after some Lenovo (or Win 10) software update, i noticed that the backlit keyboard had just 3 modes left: off, low and high. The fourth mode, automatic, which was indeed available in the preceding days, was gone.

It is no more listed in the Lenovo Settings app, and i cannot anymore choose it neither by using the app nor by cycling among modes with fn-space.

Any idea on what could be done to get back the automatic mode? Maybe there are some regedit entries to be fixed, or something like that?

Best regards and thanks in advance.

[Wall]

I add that in the device manager everything is ok, there are no yellow marks so the light sensor should be working properly: in fact, the screen brightness can still be set to automatic.

Regards