Unfortunately, I have no way to test this problem because I have no Mac machine with macOS 10.12 installed. Note that macOS 10.12 is still not supported officially, mainly for this reason. PixInsight is stable on OS X 10.10 and 10.11, both supported versions of OS X.
However, the issue you are reporting is extremely strange. The ChannelCombination tool is very simple, probably one of the simplest ones in PixInsight. There is no reason for this tool to crash, and of course it does not crash on any supported platform. Do you have an antivirus application running on your machines, by chance?