Hi Jeremy,
I had a issue with my last project where after I created a master track with the ribbons, if I selected the second of the three subsections Metro would immediately quit. I was able to expand the master track and I exported a midi file which I imported into a new Metro file and finished the project with no issues. I've gone back to the original file and I see that if I expand master track that second subsection issue is gone. If I undo the master track expansion then the same issue returns.
I was using Vienna Ensemble Pro to host 16 instances of u-he's Diva. iStat Menus shows 70% to 75% idle CPU spread evenly across the twelve Mac Pro(2009 to 5.1) cores and 5% memory pressure with my 32GB of RAM.
It could be some issue between Metro and VE Pro 5 which I know you can't really diagnose. I am running the latest version of Yosemite 10.10.5