Driver version 2.13.1 works just fine on .NET 5.0 but as soon as I ported everything over to .NET 6.0 RC1 which dropped on Tuesday and the change streams can no longer resume from the change stream from the tokens.  I reverted back to .NET 5.0 just to verify that the tokens were in fact still in the oplog and it starts back up without any issues so clearly something changed in .NET internals as to how change streams are picked back up.

Problem occurs in both Windows and Linux so it isn't OS specific.

Here is the full stacktrace

MongoDB.Driver.MongoCommandException: Command aggregate failed: Resume of change stream was not possible, as the resume point may no longer be in the oplog..
at MongoDB.Driver.Core.WireProtocol.CommandUsingCommandMessageWireProtocol`1.ProcessResponse(ConnectionId connectionId, CommandMessage responseMessage)
at MongoDB.Driver.Core.WireProtocol.CommandUsingCommandMessageWireProtocol`1.ExecuteAsync(IConnection connection, CancellationToken cancellationToken)
at MongoDB.Driver.Core.Servers.Server.ServerChannel.ExecuteProtocolAsync[TResult](IWireProtocol`1 protocol, ICoreSession session, CancellationToken cancellationToken)
at MongoDB.Driver.Core.Operations.RetryableReadOperationExecutor.ExecuteAsync[TResult](IRetryableReadOperation`1 operation, RetryableReadContext context, CancellationToken cancellationToken)
at MongoDB.Driver.Core.Operations.ReadCommandOperation`1.ExecuteAsync(RetryableReadContext context, CancellationToken cancellationToken)
at MongoDB.Driver.Core.Operations.AggregateOperation`1.ExecuteAsync(RetryableReadContext context, CancellationToken cancellationToken)
at MongoDB.Driver.Core.Operations.ChangeStreamOperation`1.ExecuteAsync(IReadBinding binding, CancellationToken cancellationToken)
at MongoDB.Driver.OperationExecutor.ExecuteReadOperationAsync[TResult](IReadBinding binding, IReadOperation`1 operation, CancellationToken cancellationToken)
at MongoDB.Driver.MongoDatabaseImpl.ExecuteReadOperationAsync[T](IClientSessionHandle session, IReadOperation`1 operation, ReadPreference readPreference, CancellationToken cancellationToken)
at MongoDB.Driver.MongoDatabaseImpl.UsingImplicitSessionAsync[TResult](Func`2 funcAsync, CancellationToken cancellationToken)

Let me know if you need any additional information/code.