Crashes and hangs can happen with any device running software, and the NetScaler is no different in this regard. While a large percentage of them get picked up during testing, the complexity involved in catching all use cases and packet combinations means that some will make their way to the Customers. The good news is that most are usually fixed by the next revision of the software. This is one of the biggest reasons to stay current in terms of NetScaler builds.
Let's first start by differentiating these crashes and hangs. While their impact on your application's availability can be the same, the underlying issues are very different, and how you have to approach them as an Administrator are different as well.