The system no longer controls the z-wave lights that I have installed. This occurred around the time that Apple iOS 8 was released. Is there a compatibility problem with iOS 8 or do I need to remove and reinstall each of the lights?
There is no known compatibility problems with iOS8.
If signals are not going through, I would first run a network rediscovery at your alarm panel.
After the rediscover, send a command to turn on one of the lights to test. Does this go through?
Are you only having trouble on your IOS8 device? Are you still able to access/control the lights directly from your panel?
If you are unable to access/control them from the panel, then a network rediscovery might help.
If you are able to access/control them from the panel then it would be something between the panel and ADC.