I think it's most likely too much sun. The brown spots look like sunburn to me. So, well done, you've taken care of the problem already. Be sure to water it less now that it's in the shade.
Jade plants are grown by many people indoors where there's never full, blazing sunlight and they do very well. So I would think outdoors, a nice shady spot would be the perfect place for them for the summer. Most plants commonly grown as house plants need at least bright shade (such as under a thin tree) when they're outside for summer vacation.
