App worked on Mac once and never again

I’ve been working on a jME3 app on a Windows machine for weeks. It’s a Griffon (Swing via Groovy) app where I have the jME canvas embedded within a Swing frame.

This weekend, I decided to try running the app on my MacBook Pro, and, to my happy surprise, it worked great. (In fact, a mesh that I never got to display on the Windows machine showed on the Mac.)

Later that day, I took my MBP home and plugged it into my Cinema Display. This time, when I ran the jME3 app, the jME window did not show anything. It just looks like a blank panel. I tried unplugging the Cinema Display and even rebooted the MBP. Nothing I’ve done has helped. It ran great that one time and not once since. There are no exceptions in the console.

This would actually be less weird if it had never worked. But that first time, it was perfect. Any ideas?