Fixed range for binary sensor include unknown value

[Ivan-Firefly]

Hi there!

I'm trying to use ploty for showing graph for my binary open/close sensor. I fixed range with the following:

layout:
  yaxis:
    range:
      - 'off'
      - 'on'
    fixedrange: true

However, for the first day graph looked ok (only on and off values were shown), but now it shows me also "unknown" value:

How could I avoid it?