nunit: Infinite loop in nunit 3.9

I am running a test suite with nunit 3.9 using nunit3-console, that randomly blocks at the end of the run. All of the tests derive from a base class that is declared with [Parallelizable(ParallelScope.All)] attribute.

I managed to break into nunit and the problem is that sometimes the NonParallel worker is stuck inside the OnEndOfShift() method of ParallelWorkItemDispatcher. The _topLevelWorkItem state is WorkItemState.Complete, and after all of the shifts have been run their queues are empty. No other worker is changing the state of the _topLevelWorkItem. Given this situation, the following code inside OnEndOfShift() is an endless loop:

// Shift has ended but all work may not yet be done
while (_topLevelWorkItem.State != WorkItemState.Complete)
{
    // This will return null if all queues are empty.
    nextShift = SelectNextShift();
    if (nextShift != null)
    {
        ShiftStarting?.Invoke(nextShift);
        nextShift.Start();
        return;
    }
}

The name of the _topLevelWorkItem is the name of the dll containing all the tests. I was not able to recreate the problem with a small set of tests but I can make investigations about variable values, execution stacks, or order of events, if you need info.