My experience is that it’s never the .ccx file that’s the problem. It’s always something else like the items I listed above. These seem to have worked in almost most cases. Another option is to right-click on the .ccx file, choose “Open with” on Mac and then choose the following:
Macintosh HD > Library > Application Support > Adobe > Adobe Desktop Common > RemoteComponents > UPI > UnifiedPluginInstallerAgent > UnifiedPluginInstallerAgent
However, restarting the computer is definitely something to try also.
Also, I’m seeing more Mac installation failures than I am Windows failures for locally installed plugins. Overall I agree with @ddbell that it installation failures seem relatively uncommon.