There are certainly non engineering problems out there... For one example, in biomedicine it's known cancer in different organs can have preference of having immune hot (in skin and lung cancer, e.g.) and cold tumors (in pancreatic and prostate cancer, e.g.), and current immunotherapy work much less well on the latter. Why this pattern exists is still an open question very important for treating patients and it's not a how did nature engineer question as it's a unintended byproduct from several tiers of complex biology involving understanding mutational burden in tumor cells, immune surveillance surrounding the tumors, and mechanical structure of the tissue, etc. The engineering payoff comes later, i.e., immunotherapy works better on a particular subset of patients, after explaining and understanding the biological phenomenon first.