When ever the router plunges or raises, it seems to leave vertical lines (along the z axis) on the workpiece. I suspect something it loose, but can’t seem to figure it out.
I use lead-ins/lead-outs on my toolpaths to help with that issue. The tool path will start at your desired distance off the main design. You do need to ensure enough waste material for the lead-ins. I normally have mine at 0.75" to 1", this way the bit eases into the cut reducing the stress on it.
What software are you using? In carveco, you can have angled or circular lead-ins and lead-outs. I’m sure Vcarve and others have something similar.
There are other methods to help with that issue but I’m not as familiar with them. I’m sure someone else will also chime in.