Illustrator 2018 clipping mask looks different on different work stations

Hello!

I'm opening a file that looks like this on my workstation (Mac Pro late 2013 running Mojave 10.14):

When my co-worker opens it on her workstation (Mac Pro late 2013 running El Capitan 10.11.6), she gets this (which I believe is actually the intended effect):

This isn't just a difference in viewing options--we're both set to Overprint Preview, and we're both running Illustrator 2018 (22.1).  When I output the file to our wide-format printer, I get the top result--when she does, she gets the bottom result.

It's almost as if a clipping is being ignored on my workstation--all that messy stuff is most likely supposed to be inside the outlined copy.  My supervisor's Mac Pro is running Sierra (not sure which number and he's gone for the day), and he gets what I get--the top result, which I believe is incorrect.

I've gone through the Preferences panes and can't find anything that might relate to this.

Does anyone have any thoughts on this?  Thanks in advance!