I have been using Illustrator to create repeat patterns for laser cutting. To do this I created a pattern swatch which I then used as a fill on a simple shape. In order to remove the hidden pattern paths (which interfere with the laser cutter) I have been expanding the selection and then using the Divide pathfinder tool, then Clean Up. This has worked every time except with one pattern which just disappears completely! When the Divide tool is used it removes the stroke from the pattern fill which then disappears with Clean Up.
The instructions I have been following are attached.
Any ideas how to fix this glitch? Hopefully thia all makes sense.