I had very similar issue a few years back on my old Auto TD5, except the following day the box was still in limp mode.
I disconnected the xyz loom from the underside, sprayed it with contact cleaner in WD or similar....was fine after that.
Must have gotten damp and caused the problem.
Can't remember if I used my nanocom to reset the fault, or us a fault with the auto gearbox only appears when there's a fault present.
HTH.