I've listened to the recordings with "d'où" at least 100 times - seriously - and made probably twice as many attempts to pronounce it. I once got a 100%, but I don't know why, and have never been able to repeat it.
I've been able to get 100% on the other words, but not d'où, so it doesn't seem like a technical problem. On the other hand, just for a sanity check, I went to google translate , gave d'où a try and it recognized it.
What else can be done to learn to pronounce d'où or something in general? I'm guessing this will come up again. Apparently, I'm not able to hear and/or reproduce something in it.