We've made sure that our Minecraft servers are as stable as possible. In their default state, with the standard vanilla launcher, you will very rarely if not ever see the server crash or restart unexpectedly. Unfortunately however, mods and plugins, especially if they're outdated, tend to cause problems. If your server is restarting or crashing, it's best to look at the logs or crash logs and see if you can find a plugin or mod listed in the crash. To prevent future crashes, ensure the plugins or mods you use are up to date with the version of Minecraft your server is running - even a plugin or mod being a couple of versions out can cause issues. If you're unable to diagnose a fix yourself, we're here to help - send us a ticket.