Unable to start Designer or Client ERROR "This Launch Jar Signature is invalid. Contact an administrator"

In ~/.ignition/clientlauncher-data there is a designerlauncher.log file.

In this file there will be a line like "Starting Java with the following parameters:" followed by a long command. If you copy/paste that into a new terminal window and run it, then get the full output and upload it here, that may help. Otherwise you can call support and they can try to help you through that process.