Occurs sometimes when an async thread initializes a new object during startup, in this case a JSONObject is being created.
An issue was already reported for this, and incorrectly closed:
https://hub.spigotmc.org/jira/browse/SPIGOT-2521
Just to clarify, PlotSquared is not trying to disable the plugin async by creating a JSONObject.
Current stacktrace:
http://hastebin.com/namadeduhu.avrasm
More Debug information:
http://hastebin.com/umolokupol.vala
Thanks.