This error was reported first in Nov 18. When importing a simple polyline drawn by hand in ArcMap there is no Import Geometry dialogue that pops up in SNAP. I have I have completed this import with the use of this helpful dialogue from other files made in the same day successfully using the same steps. Perhaps a code change that enables the request of this box at the start would resolve the issue? Also, should this code receive work it would be helpful to identify the attribute column to enable features to be assembled into symbol groups. This would classify the data by enabling a many-to-one relationship for symbols.
not every vector import is confirmed by a popup dialogue.
Are you sure that it worked for a line dataset before or was it maybe a polygon?
I had the same question once and simply mixed things up: Issues in importing vector data