if you listen to native Spanish speakers a lot, you start to notice some of the S's at the end of/in between words often sound almost non-existent (especially when they speak fast). Sometimes with other letters too, like the D at the end of ciudad. At least, that was my experience in Spain.
Yes. In Spanish, "d" is not always a strong d, sometimes it becomes like "th" in English. So you say nearly: Thormir. To conclude, it is a bit hard when you say the whole sentence to say: Quieres thormir. It is hard to eject th after an s Otherwise, it'll creat confusing in the ear of listener.
One month later, and now I can hear the "s" so maybe the poor audio reports got them to fix it. However, I have since noticed in the fast audio that the female voice frequently drops the s when the next word starts with a consonant, but you can hear the s in the slow version.