New mystery vector lines appearing on PRINT only! Not digitally on PDF or AI files.

I am having the same exact problem! were you able to fix it somehow? 

Leah,

Maybe far too far out, but I believe that you may somehow confuse/overwhelm the printer(s) with all the differently (coloured and) dashed bottom lines on top of one another, and that maybe tiny differences in the positions of the bottom lines in the PDF cause the issue on certain pages and not on others.

"extra lines appear, coming from one of the corners"

Actually, they come from multiple corners, and at least the misplaced continuation of the fourth dashed line from the right (the bold one with two shorter dashes at the end of each long dash) comes from a position further to the right from that corner.

Therefore I would suggest your making a separate print version of the final pattern set, using Save As and adding Print to the document name, and then modify it as follows:

1) Delete the bottom segment of all the dashed lines except the outermost rosy coloured bold one with the long and short dashes;

2) Leave the rosy colured bottom segment dashed or replace it by a full rosy colured line (you can drag it out with the Line Segment Tool between the end Anchor Points).

You can also just do/try it to eliminate the cause of whatever is (not) happening, and to give a nice and simple appearance in print with/withour Colours.

As I see it, the use of that (rosy) colour would give a consistent boundary to the whole set, continuing the outermost pattern line.

After that, you can go back to the final pattern set for editing or as the basis for a new pattern set, leaving the print version behind.

Can you remove the password fom your pdf?