The NonAlarmEvent function always try to Enable the condition on RefreshEnd event received.
If several notifiers are available the test is failing because it tries to Enable the conditions several times and AlreadyEnable status is returned.

As specified in part 9 §5.5.7 v1.05:
A copy of the instance of RefreshStartEventType is queued into the Event stream for every Notifier MonitoredItem in the Subscription. Each of the Event copies shall contain the same EventId.

I guess NonAlarmEvent should not change RefreshState without guard condition on previous state and might ignore identical EventId received to ignore duplicate RefreshStart/End event on several notifiers.
Moreover it does not seem absolutely necessary to Enable conditions here as the function EndTest will do that anyway, unless we only try to Enable condition for which we do not received event on refresh which is not checked.