Visual Explain Not working in MySQL Workbench
The user raising this question got an answer in the MySQL Workbench Forum: 


  Visual Explain is only available if your server supports the JSON explain output (MySQL 5.6.5 or newer). 


The reason VISUAL EXPLAIN didn't work for the user with 5.7, was the query being already prepended with explain at input time. Workbench transformed this into explain explain format=json - what wouldn't work.