This issue was reported on a few different forum posts. Simplicity Studio will crash at somewhat random times. It has been reported as happening when the debugger is launched or when editing a file and deleting several lines from it, but the behavior is not consistent.
The issue has been tracked down to the underlying SWT plug-ins in the Eclipse version on which Simplicity Studio is based. Silicon Labs is working towards updating the underlying Eclipse version, but that will not be ready for some time. In the meantime, the workaround is to replace the two swt jar files with ones that have been patched with updated SWT code. A zip file that contains the two jar files is attached to this KBA. To verify the integrity of the zip file after it is downloaded, verify the md5 of the zip file is 0665ec3711abfbf2c6355cb70fbaf73c. On a Mac from a terminal window this can be checked with the command: 'md5 swt_jar_replacements.zip'
The procedure to replace the jar files is:
1. Exit Simplicity Studio
2. In the directory [SIMPLICITY_STUDIO_INSTALLATION]/Contents/Eclipse/plugins, find the two files
3. Rename the files changing .jar to .jar-xxx, so the original files are available as a backup.
4. Extract the two jar files of the same name from the 'swt_jar_replacements.zip file to the same directory.
5. Start Simplicity Studio
Let us know if you have any troubles with the procedure or still see any Simplicity Studio crashes. Silicon Labs wishes to thank the several customers who have helped to verify the replacement jar files fix the issue.
Yes this still applies to macOS Mojave. The same jar files in the link to the KBA work with Mojave.