"Symbol already registered" exception when registering multiple notifications

[pitz-1m]

We've been seeing an occasional crash while registering a notification. The exception looks like this:

System.ArgumentException: Symbol already registered!
   at TwinCAT.Ads.TypeSystem.AdsNotificationCache.Add(ISymbol symbol, UInt32 handle, SymbolNotificationTypes notificationType, NotificationSettings settings)
   at TwinCAT.Ads.ValueAccess.AdsValueAccessor.RegisterNotification(ISymbol symbol, SymbolNotificationTypes type, NotificationSettings settings)
   at TwinCAT.Ads.ValueAccess.AdsValueAccessor.OnRegisterNotification(ISymbol symbol, SymbolNotificationTypes type, INotificationSettings settings)
   at TwinCAT.Ads.TypeSystem.Symbol.add_ValueChanged(EventHandler`1 value)
   at System.Reactive.Linq.ObservableImpl.ClassicEventProducer`2.AddHandler(TDelegate handler) in /_/Rx.NET/Source/src/System.Reactive/Linq/Observable/FromEvent.cs:line 360
   at System.Reactive.Linq.ObservableImpl.EventProducer`2.Session.AddHandler(TDelegate onNext) in /_/Rx.NET/Source/src/System.Reactive/Linq/Observable/FromEvent.cs:line 342

This seems to happen at a point where two notifications are being registered concurrently. Reading through decompiled library code... It looks like the notification handle (on which the collision occurs) is ultimately generated by the GetNextClientHandle method in TwinCAT.Ads.Internal.NotificationReceiver, which doesn't seem to be thread-safe and can generate duplicate handles. I could be way off here, only looked at it briefly.

[pitz-1m]

Looks like this is fixed in the latest release. Thanks.