I'm wondering if Vettel's issue might have been something to do with this (around the 0:24 mark):

https://www.youtube.com/watch?v=lNk9c9ddSLw

big lockup of the left front. Right before he went off at Luffield, he also locked up the left front going around Brooklands, but I don't know if that was because the tyre was already partially down (lockup around the 0:37 mark):

https://www.youtube.com/watch?v=-hxau0FEug0