It is the psych
version that is causing the difference.
This is the relevant commit: https://github.com/tenderlove/psych/commit/2422a9fc3aeff3c60c6510efbf655a34218c7605
You are about two years behind latest version, so I suggest if you can to update your dependencies on the project.
How did I find this? Using github's excellent compare function: https://github.com/tenderlove/psych/compare/v1.2.1...v1.2.2