1) It seems to happen on any .scon
2) Art is generally 100px or less. However, many art pieces feature large areas of transparency reaching up to 400 px, though.
3) Crashes happen upon opening .scml and .scon files. We are commited to the .scon format for this project, though, so I'm not sure if these crashes happen at the same frequency.
Running OSX El Capitan, v 10.11.3
MacBook Pro (Retina, 13-inch, Late 2013)
Processor 2.4 GHz Intel Core i5
Memory 8GB 1600 MHz DDR3
Graphics Intel Iris 1536 MB
Can provide crash report if you want. (It's long, figured I'd ask before posting.)