I've had this problem before and I can't remember what I did to get it to work. I have most of the image combined, but there are a few spots i am fighting with and they
won't combine. They just go to the back. I've tried putting everything on one layer, I've tried numerous other things with no luck. Hoping I can get some insight here. I attached a PDF of the file.
the white areas are what won't combine. PDF
Weld all the white elements and then select it with the Shape Cursor and Reverse Direction and then combine.
See attached.Also CDR file attached