I think I am having similar issues with my jade plant. A bunch of leaves fell off today (see picture below), even though they look relatively healthy!
The pot I have has a hole in the bottom, but after reading the advice above I think maybe the pot is too deep and I should repot with a cactus/succulent mix potting soil (currently I am using regular, organic soil). I am also worried I may have potted it with the soil too high, I don't know if that could be an issue as well. Maybe more sunlight, too. Any help would be appreciated!