How to reproduce:

• Start a server
• have a few people log in
• wait

Versions:
Torch 1.0.153.575
SE 1.181.58
Windows Server 2012 R2

It looks like it happened at the end of a long list of "Revealing grids". I will include the full torch.log as an attachment

Exception from Torch.log
2017-06-02 22:49:04.8767 [INFO] Concealment: Revealing grids: Static Grid 6164
2017-06-02 22:49:04.8767 [INFO] Concealment: Revealing grids: Military Minelayer
2017-06-02 22:49:04.9517 [FATAL] Torch: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.
at VRageMath.MyDynamicAABBTreeD.RemoveLeaf(Int32 leaf)
at VRageMath.MyDynamicAABBTreeD.RemoveProxy(Int32 proxyId)
at Concealment.ConcealmentPlugin.RevealGroup(ConcealGroup group)
at Concealment.ConcealmentPlugin.<>c__DisplayClass21_0.b__0()
at Sandbox.MySandboxGame.ProcessInvoke()
at Sandbox.MySandboxGame.Update()
at Sandbox.Engine.Platform.Game.UpdateInternal()
at Sandbox.Engine.Platform.Game.RunSingleFrame()
at Sandbox.Engine.Platform.FixedLoop.<>c__DisplayClass1.b__0()
at Sandbox.Engine.Platform.GenericLoop.Run(VoidAction tickCallback)
at Sandbox.Engine.Platform.Game.RunLoop()
at Sandbox.MySandboxGame.Run(Boolean customRenderLoop, Action disposeSplashScreen)
at VRage.Dedicated.DedicatedServer.RunInternal()
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)
at Torch.Server.TorchServer.Start()
at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

SpaceEngineersDedicated.log from around the same time
2017-06-02 22:47:49.645 - Thread: 12 -> GC Memory: 2,254,355,184 B
2017-06-02 22:48:19.654 - Thread: 12 -> GC Memory: 2,285,648,824 B
2017-06-02 22:48:37.668 - Thread: 12 -> Peer2Peer_SessionRequest 76561198067690153
2017-06-02 22:48:41.350 - Thread: 12 -> OnConnectedClient SHO attempt
2017-06-02 22:48:41.653 - Thread: 12 -> World request received: SHO
2017-06-02 22:48:41.653 - Thread: 12 -> ...responding
2017-06-02 22:48:49.669 - Thread: 12 -> GC Memory: 2,316,760,048 B
2017-06-02 22:49:04.729 - Thread: 12 -> Network readers disposed
2017-06-02 22:49:04.733 - Thread: 12 -> Logging off Steam...
2017-06-02 22:49:04.734 - Thread: 12 -> Shutting down server...
2017-06-02 22:49:04.778 - Thread: 12 -> Done
2017-06-02 22:53:41.448 - Thread: 1 -> Saving world - START
2017-06-02 22:53:41.448 - Thread: 1 -> Making world state snapshot.
2017-06-02 22:53:41.448 - Thread: 1 -> Before snapshot.: GC Memory: 2,198,209,144 B

SpaceEngineersDedicated.log.txt
torch.log.txt