the ruler? was light green, when I used Cycle, it became yellow and in both cases there were notes as well as on the region above. Then I tapped on the grey area where are the notes, the ruler? became dark green and all the notes disappeared from the piano roll area, but they are still exist on the region in the timeline. Why they disappeared, why it's good and how I can get them back and why the ruler (above the notes before the numbers that wide line) became dark green? Video is included. https://youtu.be/wBAI6APEtog

The Piano Roll shows the notes in the currently selected Regions[s] -- you're not seeing the notes in the Piano Roll because you don't have a Region selected. Simply click once on the Region to select it -- its title bar will become light green and the notes in it will appear in the Piano Roll.

How I don't have a region selected? On the track list, this instrument is active (light grey). Or do I need select track and its region aparently?

When the Track Header is light grey you have the *Track* selected -- you have to select a particular *Region* separately, by clicking directly on it.