I recently upgrade my MediaWiki install to 1.28 and upgraded ViusalEditor and Parsoid in the process. I was able to get it to work with one wiki, but it broke when I added another using the configuration example provided in the Parsoid configuration section.
Hopefully I save some people some time here with what I learn about yaml. In yaml, apparently indentation is critical it being interpreted properly, however tab characters are not allowed. If everything is configured correctly and it is not working, try checking the indentations to make sure they use spaces and not tabs.
The error I received was: parsoidserver-http-error: (curl error: 7) Couldn't connect to server.