Take long time for a alarm in Vista to appear. A change of state object in Vista is monitoring a signal on a Lon node but it takes up to 15 minutes before the alarm appears in Vista.
When a object is monitored by Vista Vista will start to poll this signal but the poll have a pretty low priority in Vista so for example graphics and trend logs have higher priority than the polling. If there is many trend logs and many signals is polled in Vista it can take a long time for Vista to go thru the poll list.
Vista can maximum read around 40 values per second.
So depending on how much other communication there is on the Lon interface it can take several minutes before Vista will see that the value have changed.
Analyze how much communication there is in Vista via a Communication log and try to reduce the communication on the Lon network interface.