4.6.21R

• Fixed MovePosition/Rotation being unintentionally cleared with velocities (#1009, #1010).
• Fixed NetworkCollider disposing of rather than pooling some collections, resulting in garbage collection.
• Fixed NetworkTrafficStatistics initializing when disabled; this did not result in tracking but did have a neglible runtime performance impact.
• Fixed NetworkTransform.GetChanged including non-synchronized properties (#1016).
• Fixed missing error log when exceeding NetworkBehaviour limit pet NetworkObject.
• Fixed prefab searching being done recursively despite being set not to (#1005 #1015).
• Fixed ObserversRpc.BufferLast not handling ExcludeOwner (#985).
• Fixed smoothers AttachOnStop not working (#1018).
• Improved NetworkTrafficStatics uses TryGetBidirectionalNetworkTraffic rather than assume value is not null. This is to resolve a Unity bug where fields lose value during debug inspection (#1000).
• Improved added additional ProfileMarkers to PredictionManager.
• Improved NetworkTransform performance marginally (#989).
• Improved added ProfileMarkers to ClientManager, ClientObjects/.RpcLinks, NetworkTransform (#989).
• Improved Writer.WriteGuidAllocated obsoleted. Allocations have been removed; use WriteGuid instead (@belplaton).
• Improved added INetworkConnectionBroadcast interface to allow broadcast mocking (#1007).
• Added ManagedObjects.OnSpawnedAdd/Remove/Clear events (#989).
• Added Beta Threaded TickSmoothers (contribution by https://github.com/belplaton)
• Added Beta Threaded Collider Rollback (contribution by https://github.com/belplaton).
• Added ability for NetworkTrafficStatistics to run in headless builds (#1004).