How can I use my existing Custom Devices with the latest ADISimRF release, given that the Noise Gain parameter is not coherent with the Gain value and the database is encrypted?

While we strive to maintain backwards compatibility when we upgrade ADISimRF, it is not a focus for custom devices. We did attempt to make old files and custom devices compatible but all cases may not be covered. Your only option is to recreate the device models. It will be a while again before we tweak the structure of the database. So hopefully you won't run into this problem again in the near to medium term.