Need some help in server crashes

[hdseventh]

I have a very confusing error i think is on world saving. This is very rare occurence, but its occured thrice in my server. Here's the error message :

TShock: ERROR: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.
  at System.Collections.Generic.Dictionary`2+Enumerator[TKey,TValue].MoveNext () [0x00013] in <533173d24dae460899d2b10975534bb0>:0
  at Terraria.GameContent.Bestiary.NPCKillsTracker.Save (System.IO.BinaryWriter writer) [0x00052] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.GameContent.Bestiary.BestiaryUnlocksTracker.Save (System.IO.BinaryWriter writer) [0x00000] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.IO.WorldFile.SaveBestiary (System.IO.BinaryWriter writer) [0x00000] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.IO.WorldFile.SaveWorld_Version2 (System.IO.BinaryWriter writer) [0x00059] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.IO.WorldFile.InternalSaveWorld (System.Boolean useCloudSaving, System.Boolean resetTime) [0x00055] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.IO.WorldFile+<>c__DisplayClass57_0.<SaveWorld>b__0 () [0x00000] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.Utilities.FileUtilities.ProtectedInvoke (System.Action action) [0x00016] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.IO.WorldFile.SaveWorldDirect (System.Boolean useCloudSaving, System.Boolean resetTime) [0x00066] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.IO.WorldFile.SaveWorld (System.Boolean useCloudSaving, System.Boolean resetTime) [0x00010] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.IO.WorldFile.SaveWorld () [0x00017] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at Terraria.WorldGen.saveAndPlayCallBack (System.Object threadContext) [0x00000] in <13c7103e4994467dac3b7e479ef8edf5>:0
  at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context (System.Object state) [0x00007] in <533173d24dae460899d2b10975534bb0>:0
  at System.Threading.ExecutionContext.RunInternal (System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean preserveSyncCtx) [0x00071] in <533173d24dae460899d2b10975534bb0>:0
  at System.Threading.ExecutionContext.Run (System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, System.Object state, System.Boolean preserveSyncCtx) [0x00000] in <533173d24dae460899d2b10975534bb0>:0
  at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem () [0x00021] in <533173d24dae460899d2b10975534bb0>:0
  at System.Threading.ThreadPoolWorkQueue.Dispatch () [0x00074] in <533173d24dae460899d2b10975534bb0>:0
  at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback () [0x00000] in <533173d24dae460899d2b10975534bb0>:0

This error happened once few months ago and twice in this week, the only plugin is more likely causing this crash is Crossplay plugin. But then again Crossplay is running flawlessly on my server for several months. It is starting to be more frequent when i set the backup interval to 180 (every 3 hours). So yeah i really don't know what causing it, as i myself is not very good at C#

The server is running on Linux, with Clean TShock 4.5.5.

[Kojirremer]

I used to have that one often as well, and I don't have Crossplay. I also barely have those after I disabled automatic backups, since they were saving more often than what I had set up, and saving takes quite a while now.
Running on Server.pro through mono.

[hdseventh]

Is this mean that there's something wrong with the auto backup? Since you experience this error without Crossplay. I need the auto backup to be prepared for any potential world destroying event like (corrupted world save, lava griefers, and hackers)