This exercise is incorrect. The lady is not pronouncing "u" in the sentence. What she really says is "Čekám matčina auta" (which is a nonsense sentence).
Granted, it is difficult to hear u at the normal speed, but it is quite clear on slow.
I didn't understand the "u matčina" part even though I am a native speaker. It should definitely be more understandable.
For me it is quite clear on the slow speed. At normal speed, it sounds rushed, but I can hear that the "u" is there. I'm a big fan of replaying a sentence on slow if I'm not sure about something.
There is nothing we can do, apart from disabling the listening exercise. But from my listening it is not that bad, I can hear the u there, even in normal speed.