Breakdown would have been caused by some grease somewhere.
I usually use disposable bags for piping royal icing to ensure there is no grease and wash everything (bowls, spatulas, tips) with warm soapy water. With the piping tips, I first soak them in boiling water after using them on buttercream.
You can make bc from the ruined icing just add shortening (1c). I have a feeling that you did not beat the icing long enough. You really need to mix on speed 3 for at least 7 min in a KA. Sometimes it looks like it is done before that for me. But if I go to use it, it melts. But since you add piping gel it won't help to rebeat now.
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