Plant 3D - creating PDF with layers

I can print a drawing (originated in Acad 2017) to a pdf with layers - all ok. Try doing a (a different drg.) in various ways with Plant 3D, but do not get any layers. Anyone any ideas as to where I may be going wrong in the set up - cannot find any differences in the drg. setup. Have attached two drawing - IO Centre layers ok, BGR drg will not layer in pdf. The attached drg. is the troublesome one

Nothing attached, as you're new to Forums your ability to attach may be limited. Can you post a link to the drawing instead?