Writing hieradata/hosts/cp4037.yaml we noticed that using an array for env_variables produces an error in PCC:

Error: Evaluation Error: Error while evaluating a '+' expression, odd number of arguments for Hash (file: /srv/jenkins/puppet-compiler/1489/change/src/modules/profile/manifests/benthos.pp, line: 31, column: 50)

As noticed by @Joe the issue resides in the env_variables hiera structure that should be an hash, instead of a list. Exceptionally, when the list contains just one element, the result is the expected one.