Oh man, as someone who has driven a tesla in the rain where the automatic wipers didn't work and I had to frantically dig through touch screen menus on the highway, this sounds all too real.
I discovered this by chance. And it seems to be subtly mentioned in the manual.
https://www.tesla.com/ownersmanual/modely/en_us/GUID-A5C33F3....
But yeah it’s weird to have to do that as half the time Auto doesn’t pick the “right” speed in the rain. Either too fast or too slow.