Your language is a little confusing.
Grouped or combined?
If they’re one path, I would break them apart. Then, either way, look for nodes that aren’t properly merged to make closed shapes like carabis said.
If they are truly just arcs (as in from the ellipse tool), then that’s a stroke and not a shape. If you’re trying to engrave them, and they are truly arcs, I would “stroke to path” them. That will give you filled shapes that will engrave as expected.
Again, without the file you’re asking us to speculate, so either upload it or understand that we’re going to flop around like fish and waste everyone’s time until we just guess correctly.