Can you import the project with the failing compositions into a new project?
Try opening that project file in CC 2014 and see if it behaves there.
I've been able to narrow it down to the 7 compositions that keep failing and the rest that don't out of about 400. I switched the compositions settings resolution to "half" 320x568. I'm noticing that if you order the compositions from top down, then they have an exponential performance. i.e.:
#1 - Master Composition Covering Everything - - haven't gotten to render
#2 - Comp right below master - - haven't gotten to render
#3 - Comp right below #2... - - haven't gotten to render
#4 - Comp next in line - - haven't gotten to render (waited 20 minutes)
#5 - Comp next in line - - renders after stalling for 6 minutes
#6 - Comp second to bottom - - renders after stalling for 2 minutes
#7 - Comp at bottom that's failing - - renders after stalling for 30 seconds
#8 - Comp that is working fine - - renders with no issues
#9 - Comp that is working fine - - renders with no issues
#10-100 Comps that are working fine - - renders with no issues
Is there a certain depth of compositions that after effects can work with? I.e., at some point do you have too many compositions?
I tried that, but to no avail. I even did a "collect files" and consolidated all footage, removed unused footage and reduced project.
Try opening this monster project in AE CC 2014. See if you can render from it.
AHHH! I found it!
So the answer to my other concern is yes. You can have too many compositions. I had to break out parts of the composition that were deeply nested and pull them up. For example, if I had "Comp A" in a bigger "Comp B", I was using sections of Comp B, and then onward and upward. So eventually, there was a "Comp P" where I really only needed that one part of "Comp A", but since I had compiled them all together like that earlier, AE had to dig deep to get to the pieces. So, per usual, it was my fault!
I am SOOO relieved to find the answer to this. The project is for an iOS front end design of an app to give custom tailored meal plans to people based on their diet, and recipes using what they have.
So in a nutshell, DON'T nest too much in AE. Take the extra 2 minutes to pull the right composition instead of the quickest grab. That would've saved me 3 days of confusion.