I don't understand Sainz's excuses in the media pen after the race. He claimed the car was "very unpredictable" and he has "no idea" why he crashed. It was clear from the replay that he braked on the white line (slippery) which caused the rear to lock and spun him around. It's an elementary mistake for a racing driver to make.
Leclerc did the same thing in the race, but saved it.
You always have to take a driver's "excuses" with a grain of salt.