Sounds like you’re trying to engrave open paths, instead of cutting or scoring them. Presumably because you have a thicker stroke? The Glowforge ignores the stroke and cuts/scores the centerline. It also tries to close your open paths, if you try to engrave an open path. You need to expand the strokes so they are filled, closed shapes.
Here are the rules I follow when using vector artwork with the Glowforge:
The Glowforge ignores stroke width. Always. When cutting/scoring it will follow the line that defines the path (i.e., what you see in Outline mode in illustrator).
Cut/Score operations follow your paths (ignoring any stroke width/pattern) and ignore fills. Both closed and open paths work.
Engrave operations ignore strokes entirely and always fill your shapes. (The color of the fill doesn’t matter. White will still be engraved. Even if there is no fill, it interior of the shape will still be engraved.)
If a path is open, the Glowforge software will close it (by connecting the beginning and end of the path) when engraving (because you can’t fill an open path), which may lead to undesirable results.
If you want to engrave the area defined by a path’s stroke, you need to use the “Outline Stroke” command to turn the stoke into a (filled, unstroked) closed path before sending it to the Glowforge.