My worst experience was coming back from Tebay in the dark... throwing it down with rain but because the motorway there has no lights and the surrounding area is dark (and even full beams won't make much difference if there's only the road for the light to hit), the cameras completely failed to function - the wipers wouldn't come on.. they couldn't see anything, because they need light to see.
I've seen less extreme versions of this many times.. darkness seems to really kill the camera.
No excuse for poor wiper performance in the dark ...but ... if it took you more than a couple of seconds to manually switch the wipers on I would be surprised. Crikey, no cars had auto wipers for most of the years cars have existed.