Somehow, a chunkholder is present in the unload queue after
it has been unloaded. It is likely that this is a result of
adding the chunk holder to the unload queue while it is
unloading. However, that should not be possible.
To find out where it is being added to the unload queue, track
the last stacktrace which adds to the unload queue and check
on chunk holder remove if the holder is present in the unload queue
and log the stacktrace.
