Apologies, I missed that it started working again for you. Since it's a mac Mini it's super puzzeling. The issue you saw might sometimes be related launching Spine on a MacBook with an external monitor. It happening in a mac Mini is very, very strange.
That said, the mini you have is the same I have, and its Intel GPU and context management driver is notoriously bad. I've spent quite a bit of time debugging issues related to that in both Spine and other apps, and the conclusion was usually to throw my hands in the air, because I can not fix bugs in the drivers myself :/