If you look at this PG https://www.babylonjs-playground.com/#165IV6#8 and by commenting out line 32 you see that the mesh is updated.
Try this with dashed lines and the updated mesh does not appear if line 32 left uncommented? https://www.babylonjs-playground.com/#165IV6#75
The option instance works with all the other meshes it should.
Have had a look at code on github but CreateLines uses the linessystem but CreateDashedLines does not.
Any advice welcome.
Perhaps one for @jerome