SystemRequirementsChecker fails with no missing requirements

It seems that the SystemRequirementsChecker.check() fails, but does not give the reason (0 requirements missing):

if (!SystemRequirementsChecker.check(appContext, new SystemRequirementsChecker.Callback() {
                    public void onRequirementsMissing(EnumSet<SystemRequirementsChecker.Requirement> enumSet) {
                        Crashlytics.log(Log.INFO, TAG, "iBeacon system check failures: " + enumSet.size());
                        for (SystemRequirementsChecker.Requirement requirement : enumSet) {
                            Crashlytics.log(Log.INFO, TAG, "Missing iBeacon requirement: " + requirement);
                        Exception e = new Exception("FYI: Problem initiating iBeacon system, services not enabled. See log for details");
})) {
   status = BeaconRangerStatus.AUTH_PROBLEM;
   return false;

The log entry shows:

iBeacon system check failures: 0

The Exception is called and logged, but no requirements are in the mum set.
How can I diagnose what the problem is?