I got a few reports that Copper 1.3 crashes on Yosemite. I am currently investigating the issue. If you cannot run Copper after an update, you can download 1.2.1 from this URL in the meantime from here.
Sorry for the inconvenience. I had to make some last minute changes as Apple didn’t approve 1.3 in the first place due to some strange macOS Sierra issues. This might have broken Yosemite support? But I am not sure.
Just keep a look at Twitter (@appfruits) or this blog.