Okay, so here's the problem from the log:
2017-12-05 10:46:54,743 [1385476] DEBUG - .ApexUnitTestRunProcessHandler - Posting the following to runTestsAsynchronous:
2017-12-05 10:46:54,743 [1385476] DEBUG - .ApexUnitTestRunProcessHandler - {"tests":[{"className":...}]}
2017-12-05 10:46:57,194 [1387927] WARN - .ApexUnitTestRunProcessHandler - Null async Apex job ID returned from queue request.
I've seen this happen a handful of times recently but am not 100% sure why. It seems to have started with Winter '18, though, when Salesforce added the ability to run tests by name instead of ID. Let me reach out to my Salesforce contacts and see if they know why that might be happening.
In the interim, I'd be curious to know if you turn off the All Tests flag on the run configuration and instead explicitly select all test classes/methods, does the same thing occur? Perhaps IC is adding something to the All Tests config that shouldn't be added? If it does occur, is there some class or method in the set of those selected that is causing this?
I'll let you know what I figure out. Thanks for providing the log!
Regards,
Scott