Yea it has something to do with the floorboards. This was posted on a different forum
The altered floors that reduce downforce affected the teams running the low-rake chassis concept the most (Merc and Aston), and Mercedes being Mercedes, as the original low-rake chassis boss, has such tremendous resources that they substantially overcame the set up and ride height issues.
Aston Martin, on limited resources, can't adopt their car as fast because it was built on someone else's philosophy, and they succeeded in the one year when copying it was a more stable decision (last year) with almost no regulation changes.
So it may take them a little more time to get it dialed in