This is a bug with the crash reporting system, which I haven’t been able to corner down so far.
Note that Apple Mail is affected too.
One solution is to totally disable crash reporting on macOS, which I may do with the next release.
To disable the crash reporter in Natron, do the following in a terminal:
mv /Applications/Natron.app/Contents/MacOS/Natron-driver /Applications/Natron.app/Contents/MacOS/Natron-driver.orig
mv /Applications/Natron.app/Contents/MacOS/Natron-bin /Applications/Natron.app/Contents/MacOS/Natron-driver