Hi, author here! At my job before Google I had to debug these kinds of bugs for our mobile robotics / computer vision stack, but I found them fun so they didn't feel "hard" per se. The most time-consuming one took a month on basically a camera-mounted computer vision system, where after an hour of use the system would start stuttering unusably. But the journey took us through heat throttling on 2009-era gaming laptops, esoteric windows APIs, hardware design, and ultimately distributed queuing. But fixing it was a blast! I learned a ton. I hated that project but fixing that bug was the highlight of it.