Failed to call hook 'OnEntityKill' on plugin 'GuardedCrate v1.9.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.GuardedCrate+EntitiesLookup.FindEventByEntity (BaseEntity entity) [0x00009] in <22776f9281e54385970028b9084f7a4c>:0 
  at Oxide.Plugins.GuardedCrate.OnEntityKill (HackableLockedCrate crate) [0x00000] in <22776f9281e54385970028b9084f7a4c>:0 
  at Oxide.Plugins.GuardedCrate.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x004db] in <22776f9281e54385970028b9084f7a4c>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <cd9a02fd331347bd82d550bb1a9c8e9f>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <b76ec77c47d1449e92b2baab8603843d>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <b76ec77c47d1449e92b2baab8603843d>:0 

server have crashed, idk if it's related or not?

Server have shutdown correctly and again the error:

Failed to call hook 'OnEntityKill' on plugin 'GuardedCrate v1.9.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.GuardedCrate+EntitiesLookup.FindEventByEntity (BaseEntity entity) [0x00009] in <91bba2e7a8424a019da12c864e1f4954>:0
  at Oxide.Plugins.GuardedCrate.OnEntityKill (HackableLockedCrate crate) [0x00000] in <91bba2e7a8424a019da12c864e1f4954>:0
  at Oxide.Plugins.GuardedCrate.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x004db] in <91bba2e7a8424a019da12c864e1f4954>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <cd9a02fd331347bd82d550bb1a9c8e9f>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <b76ec77c47d1449e92b2baab8603843d>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <b76ec77c47d1449e92b2baab8603843d>:0
Failed to call hook 'OnEntityKill' on plugin 'GuardedCrate v1.9.0' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.GuardedCrate+EntitiesLookup.FindEventByEntity (BaseEntity entity) [0x00009] in <91bba2e7a8424a019da12c864e1f4954>:0
  at Oxide.Plugins.GuardedCrate.OnEntityKill (HackableLockedCrate crate) [0x00000] in <91bba2e7a8424a019da12c864e1f4954>:0
  at Oxide.Plugins.GuardedCrate.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x004db] in <91bba2e7a8424a019da12c864e1f4954>:0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <cd9a02fd331347bd82d550bb1a9c8e9f>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <b76ec77c47d1449e92b2baab8603843d>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <b76ec77c47d1449e92b2baab8603843d>:0​

so seems not related when it crash... idk

Happens to me everytime server did daily restart. These error comes up after server is up again. Don't see any issue but error is indeed annoying

Should be resolved in the most recent update, please make sure you are on the latest NpcSpawn also.