Not exactly sure when it started but when Running tests from a run configuration, if any of the classes included in the configuration are Inactive all tests will fail with "Test Ignored"
In the log we see
2017-10-11 19:42:39,096  WARN - cloud.client.ForceComApiClient - Status code 403 returned trying to retrieve 'https://xyz--Partial.cs19.my.salesforce.com/services/data/v40.0/tooling/runTestsAsynchronous/': Forbidden
The configuration I was using previously ran without issue so it may be a regression on the Tooling API as that is where it fails.
Removing the Inactive class from the configuration solves the issue.
I would also suggest that when constructing the payload to send to the API that any class that is included in the configuration and is not active that is be excluded from the payload as a preventative measure.