Issue
When opening the workflow designer the ribbon and the actions in the workflow designer are greyed out.
Do a netwrork trace with F12 tools and you see
URL/16.0.427/Nintexforms/json.js - 404 Error
Resolution
Please contact Nintex Support and one of Support Engineers will assist you in resolving this issue.
Error Code
Fiddler trace has this error below URL/16.0.427/Nintexforms/json.js - 404 Error