dead stems are a symptom of under-watering ...but from your description, of "watering twice a week" - your dead stems may be from over-watering -
the first thing I noticed was that your soil is too dense .. meaning it (the soil) is holding too much water ...too long
cut back on watering ... to once every 5 to 7 days ....as summers grow hotter (upper 90's) increase the amount of watering
pull the entire plant from the pot ...and mix in more perlite, rocks, pebbles and sand to make the soil more "chunky" .... try to sift out the fine silt so you have a predominantly gritty potting medium ...this will be a faster draining, less water holding mix
as for the shriveled up stems ... cut them off - back to solid wood ...and new stems will emerge
