I'm pretty sure Garmin have disabled Car/Motorbike/ATV routing on purpose when using the Garmin supplied TopoActive maps in the 7XX series devices.
It could be something to do with that, or it could even a bug.
My solution to it not routing when I found out they'd deliberately disabled it in some instances was to load the Open Street Maps and use them instead, they're better than the Garmin maps for where I live and are updated more regularly.
I seem to remember some of the 'deliberately disabled' issues being activity related also, I have mine set on the Hiking activity and things that wouldn't work on others seem to work.
....
On another note, after much communication with Garmin and much testing, the issue I was having with the map freezing and not showing movement until a certain speed was reached has been fixed with firmware updates.
The 276CX also had this same freezing issue and Garmin, to their credit, fixed it with a firmware update also.
Still no solution to the encrypted firmware that I know of