When you place and construct blueprints with the blueprint control block that contain catchblocks with attachments (subgrids), another, separate timber beam inside the catchblock spawns, creating a duplicate subgrid in one catchblock. When you delete the attached block(s) and/or delete the catchblock, the game crashes with the below exception.

Yet I thought, I did already report it in here, since this issue has been present since the release of the blueprint control block. I believe this particular crash was one of the supposedly fixed issues that were released with the very last "major update" before development ended, although I confirmed that the issue was indeed not resovled.

=============================== FATAL EXCEPTION ================================
Exception occurred: VRage.MyUpdateSchedulerException: Failed to execute Void RunSingleFrame() on Medieval.MyMedievalGame
 ---> VRage.MyUpdateSchedulerException: Failed to execute Void DoUpdateAfterSimulation() on Sandbox.Game.SessionComponents.MySessionComponentLegacyUpdateScheduler
 ---> System.ArgumentNullException: Value cannot be null.
Parameter name: key
   at System.ThrowHelper.ThrowArgumentNullException(ExceptionArgument argument)
   at System.Collections.Generic.Dictionary`2.FindEntry(TKey key)
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at VRage.Scene.MyTieredComponentGroup`2.GetParent(TChildComponent child)
   at VRage.Scene.MyTieredComponentGroup`2.ChildOnParentChange(MyHierarchyComponent target, MyHierarchyComponent oldParent, MyHierarchyComponent newParent)
   at VRage.Game.Components.MyHierarchyComponent.RaiseParentChange(MyHierarchyComponent previous, MyHierarchyComponent current)
   at VRage.Game.Components.MyHierarchyComponent.OnBeforeRemovedFromContainer()
   at VRage.Game.Components.MyEntityComponent.SetContainer(MyEntityComponentContainer container)
   at VRage.Game.Components.MyEntityComponentContainer.Clear()
   at VRage.Game.Entity.MyEntity.Delete()
   at VRage.Scene.MyScene.DestroyInternal(MyEntity entity)
   at VRage.Scene.MyScene.CloseQueued()
   at Sandbox.Game.Entities.MyEntities.UpdateAfterSimulation()
   at Sandbox.Game.World.MySector.UpdateAfterSimulation()
   at Sandbox.Game.SessionComponents.MySessionComponentLegacyUpdateScheduler.DoUpdateAfterSimulation()
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates()
   --- End of inner exception stack trace ---
   at VRage.Components.MyUpdateScheduler.ReportError(Delegate action, Exception error)
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates()
   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()
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates()
   --- End of inner exception stack trace ---
   at VRage.Components.MyUpdateScheduler.ReportError(Delegate action, Exception error)
   at VRage.Components.MyUpdateScheduler.RunFixedUpdates()
   at VRage.Components.MyUpdateScheduler.RunUpdates(TimeSpan currentTime)
   at Sandbox.Engine.Platform.MySandboxUpdate.<RunLoop>b__18_0()
   at VRage.Utils.FixedLoop.Run(Action tickCallback)
   at Sandbox.Engine.Platform.MySandboxUpdate.RunLoop()
   at Medieval.MyProgram.Main(String[] args)