We had a recent support case on this subject and I wanted to cross-post the likely solution here on the forums to make it searchable.
The most common cause of instances not starting after upgrading is a license key issue. You’ll want to confirm locally that your license is able to launch a transactor on the same version. You can also look at your license expiration date by supplying the following command with your transactor properties files:
bin/datomic describe-license <transactor.properties.here>
If you require a new license you’ll need to re-build your CloudFormation json.