please check the plane zoom fill type: if you set it as Yes, it will not generate the plane copper. 

@UserSupport, I think the option for the copper plane should be "Solid" and not "No Solid". A "Yes/No" response to the "No Solid" option is confusing because answering a negative question with a simple "Yes/No" choice creates an ambiguity. Suppose you want a coffee with milk so you go into a cafe and ask for a coffee. The waiter asks you "No milk?" If you can only answer "Yes" or "No" it is not clear from the question, what the appropriate answer should be to get a coffee with milk. Is the waiter actually asking "Do you want a coffee with **no** milk in it?" In which case you would answer "No". Or is the waiter really asking "Do you want a coffee **with** milk in it?" In which case you would answer "Yes". If the waiter had asked "Milk?" then there would be no ambiguity. * Therefore the option for the copper plane should be "Solid"

@andyfierman You are right, it is confusing, we will change it next release. Many Thanks

The Correct answer to "No Solid" is "No". I regenerated Gerber files with the "NO" setting and the inner planes appeared. Andy was right on about the confusion. What added to the problem  was that all planes were present using "Export PCB design to PDF" option. Regards, H. Lin

@htlin  @andyfierman Hi It fixed at v6.1.49, Thanks