I do have several viewports in the lay-out of my drawing. They are working in my lay-out tab but when I want to plot the drawing and I look to the plot preview, I do not see some of these viewports. The viewport frame is visible but I can't see the part of my drawing.... Do I plot the drawing, the viewport is also empty. Why can I see the part of my model in a viewport at my lay-out tab but why can't I see this on my plot preview? The properties of all these viewports are the same. Same layer, color, scale etcetera.  Anybody knows?

Hello Sandervp, check out :
MAXACTVP : MAXIMUM ACTive View Port : 64 is the maximum
Clic on the not printed viewport one by one and read the properties ( CTRL + 1 ) to see the characteristics of each one ( a clic to copy the properties from one to an other won't apply everything ).
If you have a message when plotting like :
Some viewports don't match to right clic conditions. Do you want to update them before plotting :
Yes or No , don't clic on YES.

Thank you Philippe Joseph for your quick reaction. The maximum active viewport settings was standing on 16. I'd changed this to 64. After that I'd looked to the properties of every not printed viewport.I didn't see anything strange, everything was the same. After saving the drawing I had closed him. After opening again, I went to the plot preview and everything was visible. Thank you for your solution!