If the leaves fell away, that does sound rather like it could be a rot of some kind. When they are "dormant", that is deciduous, the leaves don't immediately detach at the base even if you tug on them.
The temperature in a raised bed is going to be higher than for plants in the ground so a shade cloth may indeed help, Also dark coloured media in the bed will cause a higher temperature than a lighter coloured medium. From your pictures, though, yours doesn't look excessively dark.
