If that slurry settles and dries before the clog clears (say, you give up and go to bed), the sodium acetate can crystallize and bind with the existing toilet paper and debris. What was a soft, mushy clog can harden into a concrete-like plug.
Remember sodium acetate, the salt byproduct of the reaction? It’s a white, crystalline solid. If your clog is stubborn and you pour multiple rounds of baking soda and vinegar into a stagnant bowl, you aren’t just adding water and salt. You are creating a slurry. unclog toilet baking soda vinegar