Reproduced the problem in Mill Environment
1) Curl request to modules show the release slug 'trg-dummy-0.1.0-develop'
curl http://mill.jfrog.info:12081/artifactory/api/puppet/puppet-local/v3/modules/trg-dummy -u admin:passw0rd
2)Curl request to releasee returns the following
curl http://mill.jfrog.info:12081/artifactory/api/puppet/puppet-local/v3/releases/trg-dummy-0.1.0-develop -u admin:passw0rd
{ "message" : "'trg-dummy-0.1.0-develop' is not a valid release slug" }