Starting with version 7.2.55.0, LMOS can only be deployed on an AWS Nitro-based instance type -- and in 7.2.55.0 could not be downgraded to a release prior to 7.2.55.0. Starting with 7.2.56.0, LMOS running on a Nitro instance can be downgraded to any prior release subsequent to and including 7.2.48.5.