i try to find this problem on forum, but unsuccessfully (maybe it's because of my knowledge of english). When i try to snap path to problem path, then nothing happens. But with another paths everything works perfectly.
Version 1.2.1.     
attaching screenshots below
 

Seems you have a mix of Bézier- and Spiro-Path. Is this by intention?

it's intentional. but there is nearby one more Spiro-Path, with which snapping works correctly. Does it matter which paths (Spiro or Bezier) are using?

Not in front of my comp right now, but I guess you need to enable a desired snapping option. Have you been there already?

I don't fully understand what option you are talking about. There is a screen, where snapping works with another spiro path, but still didn't work with problem path

What does  the Staus Bar tells about the Problematic Path when it's selected with the Selection tool (S)?

i think, that's a status bar at the bottom of the screen. Here a screenshot

so my time is 1 a.m, I will answer you the next morning. Thanks

Please upload the file - it´s really hard to investigate from here.

I suppose the cyrillic words on your screenshot mean "handle to path" and not any other item of the path snapping options.

David_CAU, yes, it's mean ''handle to path''. Is it not a snapping option? maybe i misunderstood you.

Polygon, i upload below a file. Problem path is located on the right side of the document, with red stroke

The problematic Path is a Spiro Path Object. You´re trying to snap a Spiro Path to another Spiro Path and that will just work with snapping to the initial nodes, because the stroke is just a visual approximation of a curvature which will work like a normal curve only after conversion to a stroke with Path->Object to Path. It seems you have drawn the whole map with the Spiro Path effect instead of Bézier Path.

I need to redrawn this path as Bezier, then snapping will start working with this path? I tried to do that  Path->Object to Path, but notching happened. Also, i don't understand why snapping works with same spyro line, closed and not closed. 

Maybe, there is some possibility to transform Spyro line to Bezier? 

eziik

Maybe, there is some possibility to transform Spyro line to Bezier?

Yes - as I said: Path->Object to Path will convert Spiro into Bézier. Why snappingt "seems" to work on the other Spiro path is because of its node density:

I transform Spyro to Bezier, but notching happened, snapping to path still not working. But i turn on snapping to smooth nodes, and it started snapping to the any path, Bezier and Spyro. I needed snapping to path, but thanks to your attachment I saw another option that works. Thank you