I do notice the waffle structure and this should be reported to DxO support.
I also noticed that your stunning photo was shot at ISO 640 and using DP XD might not be worth it due to noise to processing time ratio. If any noise reduction at all is needed to be applied, Deep Prime would be more then enough.
But that said, I’m one of those who don’t mind some luminance grain in the shots. They build character!
I find XD can introduce artefacts in smoother areas when the noise is strong. In such cases, I will try negative values on Noise model to address the issue. You lose some clarity in detail areas, but it can tame the issues.
I generally try multiples of -15. Usually -30 or -45 will sort the problem, but occasionally I will go to -60 and once or twice to -75.
Then again… on the photo you have shown, I would just use DeepPRIME and not worry about DeepPRIME XD. Unless you’re printing it very large.