It looks like this indikator shows only 100% or signal lost. And if I look at signal in AirData, I see only 100 or 0. Is it correct or not?

Do you mean WIFI strength ? I once had 75% before signal was lost completely. This I saw later in the log, during flight I only noticed that the signal strength symbol was "not good". So I had a score of 96.6

At me it's pretty the same behavior. Not sure about the airdata entries, but according to the signal strength indicator in the app it's indeed either 100%, then maybe very short time 75% or suddenly 0%.

I’ve seen mine at varying levels. Anywhere from 25%, 50%, 75% and 100%. It’s at 100% more than anything though.