I created a file with a mm grid with thicker cm lines. I created a small part of the grid and used pattern fill. In Inkscape it looks o.k., but when I print (to pdf) or save to pdf the pattern fill is not displayed correctly.

I had a similar problem before and got it fixed by combining the paths, but if I do that on this file the thicker cm lines disappear because all lines get the same stroke width.
This is my .svg file
https://www.dropbox.com/s/02vj3ng1l52xtdy/Testcentrum%20A4%20grid%20mm%20%2B%20rulers%20alt.svg?dl=0&s=sl
Does anybody know how I can fix this? Thanks in advance.