Dlaczego zniknęły mi piętra?

Probably beause your device lost connection to the phone, and did not sync. Sync over the USB cable, or use the Sync / Connection Troubleshooting Guide to fix the problem.

Wszystko już robiłam bez rezultatu.

Ah, sorry, I have overseen you spoke about floors counting. In that case verify that the barometric altimeter on your device works all right (the pressure sensor hole may be clogged with an obstacle or dirt). And have a look at these tips: What's the secret to tracking stairs accurately?

Niestety, bez zmian.

Niestety, bez zmian.

And did you check whether the barometric altimeter works?

A jak to sprawdzić :-(

Nie znam się za bardzo na tym ale na początku wszystko było.

A jak to sprawdzić :-(

Have a look at the document: Steps to Calibrate the Barometric Altimeter on the vivoactive 3 Series Watch

And also at the forum thread: Clean altimeter holes

ale na początku wszystko było

Yes, many things work fine when they are new, but work worse when they are older, especialy if no maintenance is held. Washing the watch regularly, and keeping the pressure sensor hole clean is important for its functionality.