Workers stuck on BlockingResultHandler.getResult

In a third issue for running tests on Appveyor where TestKit is involved which then runs tests utilising worker daemons I get tests failing bdue to this issue. Note the timeout is coming from @Timeout of the Spock Framework. (I don;t have tests taking this long on a local Windows installation).

A first glance seems that the processes are stuck on a lock waiting for workers to become available. Is still possible?

Method timed out after 360.00 seconds
	at java.util.concurrent.locks.LockSupport.park(
	at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(
	at java.util.concurrent.ArrayBlockingQueue.take(
	at org.gradle.tooling.internal.consumer.BlockingResultHandler.getResult(
	at org.gradle.testkit.runner.internal.DefaultGradleRunner.buildAndFail(