This is the message I get in my console.
Failed to call hook 'OnEntityDeath' on plugin 'PlayerChallenges v2.0.52' (NullReferenceException: Object reference not set to an instance of an object.)
  at Oxide.Plugins.PlayerChallenges.OnEntityDeath (BaseCombatEntity entity, HitInfo info) [0x00352] in <4bfc0ac73000442e9488a97ebc84e9a1>:0 
  at Oxide.Plugins.PlayerChallenges.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00e88] in <4bfc0ac73000442e9488a97ebc84e9a1>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <d4a0be71194349e98f7b43231b9cea3b>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <b974d7a025404888bcdd55b51f29c440>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <b974d7a025404888bcdd55b51f29c440>:0  
(Filename: ./Runtime/Export/Debug/Debug.bindings.h Line: 35)

seems the same as mine, so i just add this here:

(06:50:17) | Failed to call hook 'OnEntityDeath' on plugin 'PlayerChallenges v2.0.52' (NullReferenceException: Object reference not set to an instance of an object.)

at Oxide.Plugins.PlayerChallenges.OnEntityDeath (BaseCombatEntity entity, HitInfo info) [0x00352] in <916b0b3568db4d2cacf4ffced6ca766e>:0

at Oxide.Plugins.PlayerChallenges.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00e88] in <916b0b3568db4d2cacf4ffced6ca766e>: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

(06:50:17) | Calling kill - but already IsDestroyed!? innertube.deployed[0]

I found this in my server logs

Failed to call hook 'OnEntityDeath' on plugin 'PlayerChallenges v2.0.52' (NullReferenceException: Object reference not set to an instance of an object.)

  at Oxide.Plugins.PlayerChallenges.OnEntityDeath (BaseCombatEntity entity, HitInfo info) [0x00352] in <1e5f6643ceea49678771f4223e452f84>:0 

  at Oxide.Plugins.PlayerChallenges.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00e88] in <1e5f6643ceea49678771f4223e452f84>:0 

  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <87ce9ac9776a48658bc55eae6debe38b>:0 

  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <b6d06fce9e044af4a6ddc8d724bd3b0b>:0 

  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <b6d06fce9e044af4a6ddc8d724bd3b0b>:0 

Calling kill - but already IsDestroyed!? storageadaptor.deployed[0]