Printing issues through Layout "export" vs printers PDF convertor

I have solved this, or I think so, but just in case someone has a better idea or comes across the same problem: after exporting with Layout “export” in the File menu, neither in my printers preview, not in the actual printing, the lines are visible or printed. But if I create the PDF using the printer menu, then all works correctly. I don’t know where is the problem or if it is me who is doing something wrong, but since I have found a way out, then all good so far. However, if there’s something I am doing wrong when using the correct Layout command, I would like to learn about, please.
Graphic regards to all of you! JC