It was the song choice for both, I think. Misha's sob story put her through, the public seem to be weirdly infatuated with Janet and then Little Mix and Marcus were just good enough to get their places.
There's probably some voter fatigue in that it's the third time in about seven days she needs support. Plus I think a lot of people tend to swallow the judges' comments verbatim hence ambivalence whether she sang a little known song that was too big for her.
It just shows that DS isn't representative of the wider audience. You'd think she was going to win after Gary's comments both weeks and the seal of approval from Bryan Adams.