I upgraded from 1.8 series to 1.9.2 yesterday. With 1.8 I was able to get environments informations with the API by doing a GET with environment name, for example with curl:
curl -k -u user:secret -H "Accept: version=2,application/json" -H "Content-Type: application/json" https://foreman.mydomain/api/environments/production

Since the upgrade, I am only able to query environment with id:
curl -k -u user:secret -H "Content-Type: application/json" https://foreman.mydomain/api/environments/production
return "message": "Resource environment not found by id 'production'"

I sent an email to users mailing-list and Dominic told me to open an issue and it might be linked to #11037

Thank you