Unable to Snap to section lines?

After I create a section I am unable to snap to the lines created. Is this normal ?
Rhino for Mac

Tim, have you checked the OSnap settings?

Yes. Have tried all different combinations. Some curves act as normal and snap but many do not

Once I move curves to a new file Snap works again

Is there a fix in the original file ? Not ideal to work on another file.

If that’s happening on a single file, can you post the sample file here?