Never saw Fed wear the vest outside. Just having the vest handy probably means the problem is still there and he was prepared for it. Not good.
He had plenty of time to take care of the problem but it wasn't enough apparently.
They said the temperature drastically went down in Hamburg after the sun set. Once they closed the roof, Roger took the vest off.
FFF said the serve speed was slow, but maybe it's the new racket.
Fed needs to get used to it before really being able to push it.
That's what I'm thinking anyway.
It could be that Fed had the forecast and was prepared with the vest.
All in all, he's doing OK I would guess for not having good form at Wimbledon, having a new racket and then playing on clay.
We'll get a good look at him once he plays the HC masters.