I've noticed something similar, DDG has been increasingly ignoring my keywords, especially when I put quotes around them, and returning irrelevant results. It used to be that if you had two words with quotes around them it would tend to return results with both keywords, now it seems to return results with only one of the keywords. I think the scope of searches has declined also, I can search for things I know exist and DDG won't find them. The more marginal the search, on the fringes outside of what is most popular, the less capable DDG seems to be in finding results. Maybe they shrank the size of their database or excluded a lot of the less connected sites from their search?