By the color it looks like rot is involved. Pull off all dead decaying material, and keep the mulch back. What I do is... one part hydrogen peroxide(on the shelf 3 %) to 3 parts water. Pour it all around the ground and on the fans etc. That kills all bacteria...good and bad. Let it dry out. You want everything bad to die...the good bacteria will come back. If there are any healthy parts below the soil the H202 just converts to extra oxygen. Protect it from getting too wet, rain or watering... put a clear plastic container over it just when moisture is in the air. Otherwise you want plenty of air circulation. Spray it every few days, (do not soak it) with 10 percent hydrogen peroxide mix. Hopefully, it will improve.
But if you have been using bleach you might have a chemical reaction.
So then not sure what you should do. Sorry.
Many blessings for your success!
