The technical explanation/setup change that caused the tire issues:
"Mercedes went into this race more concerned than the outside world might have imagined, given how comfortably it had locked out the front row, Bottas ahead of Hamilton this time.
Its concern was always tyre behaviour in the very high temperatures forecasted for race day. It had struggled in such conditions in the Friday practices of the Styrian and British GP weekends. But this time it had looked very strong in the high temperature race runs of Friday afternoon.
Yes, but the Mercedes were eating through the left-front. So their set-up into Friday sought to protect that tyre – and in so doing transferred more of the load onto the rears. Turns out, there just wasn’t the capacity there for the rears to accept that increased burden."
https://the-race.com/formula-1/the-merc ... defeat-it/
Now, how to solve the problem of making sure the W11 isn't getting blisters on either the front or rear tires is the engineering challenge that the team is going to have to make progress on before Sunday in Barcelona. The re-appearance of the C1 will surely help Mercedes a bit, but they can't always rely on optimum temperatures or the hardest compounds.