Home Assistant OS
The table in this post helps to clarify the four major ways of installing Home Assistant.
That’s the Native API component so you’ve confirmed all of the Sonoff devices have it (including the one that isn’t discovered).
At this point, I’m at the limit of my knowledge of ESPhome so the only thing left is to confirm the one that can’t be discovered had a unique name and isn’t identical to one of the other devices that is discovered. Beyond that, someone with more knowledge will have to help you.