NetworkManager Error 3

18.11 00:55:18 [Server] WARN Exception in thread "Craft Scheduler Thread - 3"
18.11 00:55:18 [Server] WARN org.apache.commons.lang.UnhandledException: Plugin NetworkManager v2.8.3-SNAPSHOT generated an exception while executing task 4121
18.11 00:55:18 [Server] INFO at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
18.11 00:55:18 [Server] INFO at org.github.paperspigot.ServerSchedulerReportingWrapper.run(ServerSchedulerReportingWrapper.java:23)
18.11 00:55:18 [Server] INFO at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
18.11 00:55:18 [Server] INFO at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
18.11 00:55:18 [Server] INFO at java.lang.Thread.run(Unknown Source)
18.11 00:55:18 [Server] INFO Caused by: java.util.ConcurrentModificationException
18.11 00:55:18 [Server] INFO at java.util.LinkedHashMap$LinkedHashIterator.nextNode(Unknown Source)
18.11 00:55:18 [Server] INFO at java.util.LinkedHashMap$LinkedKeyIterator.next(Unknown Source)
18.11 00:55:18 [Server] INFO at org.bukkit.plugin.java.JavaPluginLoader.getClassByName(JavaPluginLoader.java:189)
18.11 00:55:18 [Server] INFO at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:98)
18.11 00:55:18 [Server] INFO at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:87)
18.11 00:55:18 [Server] INFO at java.lang.ClassLoader.loadClass(Unknown Source)
18.11 00:55:18 [Server] INFO at java.lang.ClassLoader.loadClass(Unknown Source)
18.11 00:55:18 [Server] INFO at java.lang.Class.forName0(Native Method)
18.11 00:55:18 [Server] INFO at java.lang.Class.forName(Unknown Source)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.Util.getInstance(Util.java:408)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.SQLError.createSQLException(SQLError.java:919)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.SQLError.createSQLException(SQLError.java:898)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.SQLError.createSQLException(SQLError.java:887)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.SQLError.createSQLException(SQLError.java:861)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.ConnectionImpl.throwConnectionClosedException(ConnectionImpl.java:1192)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:1187)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.ConnectionImpl.versionMeetsMinimum(ConnectionImpl.java:5202)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.Field.isOpaqueBinary(Field.java:723)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.ResultSetImpl.getObject(ResultSetImpl.java:4519)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.mysql.jdbc.ResultSetImpl.getObject(ResultSetImpl.java:4696)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.lib.hikari.pool.HikariProxyResultSet.getObject(HikariProxyResultSet.java)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.common.modules.NMCachedPunishments.getPunishmentFromResultSet(NMCachedPunishments.java:470)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.common.modules.NMCachedPunishments.reload(NMCachedPunishments.java:88)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.spigot.managers.cache.NMCacheManager.reload(NMCacheManager.java:56)
18.11 00:55:18 [Server] INFO at nl.chimpgamer.networkmanager.spigot.managers.cache.NMCacheManager.lambda$null$0(NMCacheManager.java:67)
18.11 00:55:18 [Server] INFO at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftTask.run(CraftTask.java:59)
18.11 00:55:18 [Server] INFO at org.bukkit.craftbukkit.v1_8_R3.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
18.11 00:55:18 [Server] INFO ... 4 more