Every now and then when the server is shutting down or starting up (I forget if it's both or just one or the other), the shutdown/startup process is halted. I check the logs and I can see that this halting occurs when the Minepacks plugin is being enabled/disabled. Specifcally the halting occurs on the update checker part of the process. I'm assuming the plugin sometimes is not able to contact a site and as a result, the plugin disabling/enabling process can't continue, which then halts the startup/shutdown process. Usually plugin devs move their network stuff off the main thread because if it's on the main thread and a connection can't be reached, it just causes chaos. Update checker does not need to be on the main thread.

The update check isn't on the main thread.
However, on shutdown it will wait for it to finish, preventing broken updates in case someone kills the server early.
I guess I could add a config option to not check for updates on shutdown. Also, maybe reduce the timeouts for the checks.