With regards to Stroll, Racing Point are reporting that there was underside damage to the front spoiler, causing loss of downforce - which they could see on the telemetry but not understand until they got it back into the garage. It would certainly explain his loss of form after a really good first half of the race.
One of the things I find telling is that Lewis could have parked the car up and still become World Champion again yesterday, but of course that isn't his mental make-up. I think he was taking a relatively cautious approach early on / saving the tyres as much as possible? - a bit like Sutton biding his time on Turkington until he knew a pass was 100%
- but he was certainly prepared to take the chance on almost destroyed tyres when the team were urging him to come on for an "almost" certainly safe stop which would leave him (just) in the lead.