Hi, since you are on a Mac, there are some known Mac app store Apps that make myDMX 3 software behave oddly or free/crash. Do you have any of these apps installed or similar?
Magnet
Flexiglass
Popclip
BetterSnapTool
Cinch
TextExpander
If so, try uninstalling it and see if that clears up the issue. Let me know thanks!