First issue seems to be with a group rank change requirement. Probably missed something but..

25.04 03:05:43 [Server] INFO [Vault] Checking for Updates ...
25.04 03:05:44 [Server] INFO [Vault] No new version available
25.04 03:05:48 [Server] WARN Exception in thread "Craft Scheduler Thread - 0"
25.04 03:05:48 [Server] WARN org.apache.commons.lang.UnhandledException: Plugin Autorank v3.7.3 generated an exception while executing task 16
25.04 03:05:48 [Server] INFO at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
25.04 03:05:48 [Server] INFO at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
25.04 03:05:48 [Server] INFO at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
25.04 03:05:48 [Server] INFO at java.lang.Thread.run(Thread.java:745)
25.04 03:05:48 [Server] INFO Caused by: java.lang.IllegalArgumentException: Requirement 'rank change' of group 'Member' is unknown!
25.04 03:05:48 [Server] INFO at me.armar.plugins.autorank.rankbuilder.ChangeGroupBuilder.initAdvancedConfig(ChangeGroupBuilder.java:204)
25.04 03:05:48 [Server] INFO at me.armar.plugins.autorank.rankbuilder.ChangeGroupBuilder.initialiseChangeGroups(ChangeGroupBuilder.java:52)
25.04 03:05:48 [Server] INFO at me.armar.plugins.autorank.rankbuilder.ChangeGroupManager.initialiseFromConfigs(ChangeGroupManager.java:47)
25.04 03:05:48 [Server] INFO at me.armar.plugins.autorank.Autorank$1.run(Autorank.java:352)
25.04 03:05:48 [Server] INFO at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftTask.run(CraftTask.java:71)
25.04 03:05:48 [Server] INFO at org.bukkit.craftbukkit.v1_9_R1.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
25.04 03:05:48 [Server] INFO ... 3 more

Here's my config file:
[http://pastebin.com/gaWbYE8n]

Second is an error that happens with the /ar commands. The /ar commands work fine for a couple mins, then something goes wrong with:

25.04 03:08:39 [Server] ERROR null
25.04 03:08:39 [Server] INFO org.bukkit.command.CommandException: Unhandled exception executing command 'ar' in plugin Autorank v3.7.3
25.04 03:08:39 [Server] INFO at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46) ~[spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) ~[spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at org.bukkit.craftbukkit.v1_9_R1.CraftServer.dispatchCommand(CraftServer.java:645) ~[spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.PlayerConnection.handleCommand(PlayerConnection.java:1350) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.PlayerConnection.a(PlayerConnection.java:1185) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.PacketPlayInChat.a(PacketPlayInChat.java:45) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.PacketPlayInChat.a(PacketPlayInChat.java:1) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.PlayerConnectionUtils$1.run(SourceFile:13) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_77]
25.04 03:08:39 [Server] INFO at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_77]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.SystemUtils.a(SourceFile:45) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.MinecraftServer.D(MinecraftServer.java:721) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.DedicatedServer.D(DedicatedServer.java:400) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.MinecraftServer.C(MinecraftServer.java:660) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at net.minecraft.server.v1_9_R1.MinecraftServer.run(MinecraftServer.java:559) [spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at java.lang.Thread.run(Thread.java:745) [?:1.8.0_77]
25.04 03:08:39 [Server] INFO Caused by: java.lang.IllegalArgumentException: No enum constant org.bukkit.entity.EntityType.MOBS
25.04 03:08:39 [Server] INFO at java.lang.Enum.valueOf(Enum.java:238) ~[?:1.8.0_77]
25.04 03:08:39 [Server] INFO at org.bukkit.entity.EntityType.valueOf(EntityType.java:1) ~[spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO at me.armar.plugins.autorank.playerchecker.requirement.MobKillsRequirement.getDescription(MobKillsRequirement.java:37) ~[?:?]
25.04 03:08:39 [Server] INFO at me.armar.plugins.autorank.rankbuilder.holders.RequirementsHolder.getDescription(RequirementsHolder.java:153) ~[?:?]
25.04 03:08:39 [Server] INFO at me.armar.plugins.autorank.playerchecker.PlayerChecker.getRequirementsInStringList(PlayerChecker.java:172) ~[?:?]
25.04 03:08:39 [Server] INFO at me.armar.plugins.autorank.commands.CheckCommand.check(CheckCommand.java:238) ~[?:?]
25.04 03:08:39 [Server] INFO at me.armar.plugins.autorank.commands.CheckCommand.onCommand(CheckCommand.java:294) ~[?:?]
25.04 03:08:39 [Server] INFO at me.armar.plugins.autorank.commands.manager.CommandsManager.onCommand(CommandsManager.java:159) ~[?:?]
25.04 03:08:39 [Server] INFO at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44) ~[spigot-BT52_04_24.jar:git-Spigot-e6f93f4-7a6b143]
25.04 03:08:39 [Server] INFO ... 15 more

Help on this is, of course, appreciated.

The first issue is caused by the fact that you don't have 'results' for the Member group. The rank change, command and message are all in the requirements part, but they should be in the results part. (look at your other groups, those are configured correctly)

The second issue I'm still investigating on.

I found the issue and will fix it. Expect a new dev build for you soon!

Could you use dev build 521? http://62.131.38.74:8080/job/Autorank/521/

Ah haha, figured I missed something.

Dev build did not solve the issue.

Hmm, it did not? Is it still showing the same error?

Yeah, exact same error log in console.

I removed it from my server, I should've copied/pasted it again just in the case there was anything slightly changed in it. But it appeared exactly the same. When I get a chance I'll try it out again and post the console log for you.