Before Build 31, I had 2 profiles - Cycling and Walking.
Most of the time it was on Cycling. Outside my house, I'd open BT, select a route to load, hit the GPS button and, within a second or so, the Start button would be active.
Now I have Build 31. I Duplicated the 2 Profiles to make 4 - 2 for MPH and 2 for KPH.
Today I went for a walk using the new Profiles for the first time.
Outside my house, I opened BT, selected a route to load, hit the GPS button and ... no active Start button. I waited 20 seconds or so but no change.
I then selected another Profile from the front screen and bingo ... from there it worked as fast as normal.
I tried this using each of the 4 Profiles as the one which was already selected when I opened BT and they all behaved the same.
I also tried rebooting the phone, but same result.
To summarize, a Profile needs to be selected before starting a route. It doesn't seem to matter whether a Profile is selected before or after selecting a route.
In other words, the default / last used Profile doesn't automatically work any more. You have to manually select one before the Start button is active.