It’s definetly a problem of satellite imagery not having any ground details in mountain shadows.
If you look southbound the valley to the north of Castello di Sasso Corbaro all the shadows on the northsides of the hills have no detail whatsoever:
World map:
There are a couple ways they could fix these:
- Make an Algorithm to generate some type of generic mountainsides and replace the no-detail area with it, like they do with the generic countryside patches they add when there’s no detail because of cloud coverage. But that’s probably a lot of work, or they do it already, but with a rather dull result.
- Avoid satellite imagery that has no detail in shadows of big objects like mountains. But that may mean to make a decision between using lower res image data with more consistent detail and high res image data with (in worst case) patches of missing data like in the shadows here.
Well, it might be newer data, but that doesn’t mean it’s better data. 
Edit: BTW this was without WU18 installed, just to test.