[Mondaveo]

Probably a temporary glitch in some computer system - it may have seen a parameter or sensor value it didn't like, that made it impossible to continue automatically and needed a manual restart.

I had a similar experience years ago, where the dash spontaneously displayed the message "Transmission limited function" and the gearbox went into neutral. Pulled up, shut down and restarted the engine, and all was back to normal. It never did it again (although I went on to have other gearbox symptoms). We subsequently found out that one of the gearbox input speed sensors was bad and had to be replaced.

It'd likely be possible to see more information by connecting an OBDii scanner and retrieving the fault codes, but without it we know no more than the message on the dash; and if you didn't do it at the time of the fault then there probably is no record of it kept after restarting (there wasn't in my case).

According to the Mighty Car Mods crew, VAG vehicles (VW, Audi) do keep a historical record of fault codes, so there might be a reason to get one of them if you're the kind who likes to get to the bottom of every warning and error message...