How did you make it? Configuring 900 degrees in iRacing and lowering it in the drivers or configuring 490 degrees in the sim? If it's the latter you messed up the steering linearity so I would be surprised if you could control the car trying to drift.
I've never experienced it in RUF nor McLaren. Maybe you're releasing the paddle to fast - after the gear disengages but before it engages next gear? There are definitely people who doesn't experience the problem so it's down to their inputs.
ActualGrip=(1-wear)*MaxGrip + some kind of linear parametrization of grip with temperature
Like it is done in most other sims?
I'm sure that their ultimate goal is make the core features of the tire so solid, that they could concentrate on things like vulcanization, blistering, flat spots, etc.