The projected opening stint length was 12 laps worst case scenario and 14/15 laps best case, so the 11-lap stints run by Lewis and Valtteri were close. But Lewis was on the radio as early as lap 7 explaining that the tyres were 'fragile.'
On Lap 9, both Lewis and Valtteri's lap times dropped off significantly and it was evident that the Silver Arrows had lost UltraSoft performance earlier and more significantly than their rivals, hence the early double-stop, achievable because Valtteri had dropped 10s behind Lewis.
At this point, Verstappen's pace looked too hot to handle but after the first stops (the Ferraris ran to lap 17), Lewis still ran second, ahead of Ricciardo and Vettel, hoping that the performance on the SuperSoft would be better.
It wasn't. Just 10 laps into the stint Lewis was reporting that the tyre wasn't great: "I'm struggling, man!"
Almost simultaneously, Ricciardo was telling Red Bull that he could feel issues with the left front tyre.
Graining was a problem for everyone, but to different degrees. Factors such as track / tyre temperature, set up and driving style all influence graining which, put simply, occurs when the lateral forces are high enough that rather than sticking, the rubber starts to break up.
The fronts usually suffer worst because they are worked harder through the steering inputs, which leads to less grip and the feeling that the grippier rears are pushing the fronts on - understeer - with an attendant drop-off in lap time.