Answer: This is an interesting problem! I would first check that there is no water sitting in the drainage saucer beneath the draceana. Then I would check to be sure the drainage holes in the container are functioning. Sometimes waterlogged soil can eventually smell bad.
Then I would carefully examine the plant and see if any area on the stem might be rotting. Check too if you have a cat, to see if it may have used the soil surface as a litter box.
Next I would gently unpot the plant and carefully examine the potting mix -- wearing gloves or sorting through it with a trowel. Perhaps something foreign became encorporated in it.
If that doesn't reveal anything, you might contact the potting mix company and ask if they are aware of any unusual problems with it. I hope you can locate the source soon!
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