Likely when a delayed effect is scheduled and then the entity is removed.

System.NullReferenceException: Object reference not set to an instance of an object.
   at Sandbox.Game.Entities.Entity.Stats.Effects.MyDamageOverTimeEffect.Activate(MyEntityStatComponent owner)
   at Sandbox.Game.Entities.Entity.Stats.MyEntityStatComponent.AddEffect(MyDefinitionId effectDefinitionId, Int64 applicantEntityId)
   at Sandbox.Game.Entities.Entity.Stats.MyEntityStatComponent.ApplyOperation(MyEffectOperation effect, Int64 applicantEntityId)
   at Sandbox.Game.Entities.Entity.Stats.MyEntityStatComponent.DelayedEffect.HandleTick(Int64 interval)
   at Meds.Wrapper.Metrics.UpdateSchedulerMetrics.TimedUpdatePatch.Profile(MyTimedUpdate update, Int64 dt) in <MEDS>\Meds.Wrapper\Metrics\UpdateSchedulerMetrics.cs:line 153
   at VRage.Components.MyUpdateScheduler.RunTimedUpdates(MyUpdateScheduler this) in patch
VRage.MyUpdateSchedulerException: Failed to execute Void HandleTick(Int64) on Sandbox.Game.Entities.Entity.Stats.MyEntityStatComponent+DelayedEffect
   at VRage.Components.MyUpdateScheduler.ReportError(MyUpdateScheduler this, Delegate action, Exception error) in patch
   at VRage.Components.MyUpdateScheduler.RunTimedUpdates(MyUpdateScheduler this) in patch
   at VRage.Components.MyUpdateScheduler.RunUpdates(TimeSpan currentTime)
   at Sandbox.Game.World.MySession.UpdateComponents()
   at Sandbox.Game.World.MySession.Update(MyTimeSpan updateTime)
   at Sandbox.MySandboxGame.Update()
   at Sandbox.Engine.Platform.Game.UpdateInternal()
   at Sandbox.Engine.Platform.Game.RunSingleFrame(Game this) in patch
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates(MyUpdateScheduler this) in patch
VRage.MyUpdateSchedulerException: Failed to execute Void RunSingleFrame() on Medieval.MyMedievalGame
   at Meds.Wrapper.ServerService.Run() in <MEDS>\Meds.Wrapper\ServerService.cs:line 65
   at System.Threading.Tasks.Task.Execute()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at Meds.Shared.HostBuilder.HostImpl.<StopOnBackgroundTaskFailure>d__8.MoveNext() in <MEDS>\Meds.Shared\HostBuilder.cs:line 110