Coveo Admin kept throwing this error:
Cannot connect to the instance default of Coveo Enterprise Search hosted on localhost port 52800.
Check for following current problems and try again :
The Coveo Enterprise Search service may not have been started.
You may not have administrator rights.
The Coveo Enterprise Search service log on account may have changed.
Turns out the problem was one of the index sources was pointing to a url that was not accessible.