I had this sort of thing at work the other day.
Was testing the reversing camera was working - and it wasn't.
So my initial thoughts were to fix the reversing camera. After wasting my time climbing ladders to the top of the van, stripping the covers off the camera and following wires.... I then wondered why the beeping wasn't occurring when in reverse, and then checked the reverse lights to see they were not working either.
The van was going for a service after my checks, so left it and asked them to check the reverse wiring on the gearbox. Turns out it was not connected. Turns out, the van had just had its gearbox replaced and the reverse wiring had not been reconnected.
Not sure where the 1st and reverse connectors are on the Jatco, but if they're the same shape and close, they could quite easily have been swapped over by some work done.