Yes, you are correct, it is because you used the half hard wire. Your wire will get more brittle and break the more and more you coil and twist it. You will not see the same result with the dead soft wire.

I find that soft wire works for most things. It is also easier on the hands when you coil it.

The major issue I face with long lengths is the kinking. To solve it, I hold the wire similarly to the way you would when you crochet or knit. That way it runs through your fingers instead of kinking.

Thanks for the input. I tried fine silver, because my bead store didn't have dead soft. Much better results. I'm trying to guide the wire like you suggested to keep the kinks at bay.