More seriously, the absolute worst developer experience I've ever had was a weird proprietary environment called "OpenAT" for a mobile module system. Admittely we were in the beta programme because we needed features, but every new firmware update would fix some features of the operating system and break others. At one point while trying to debug terrible sound we noticed that the volume control wasn't at all linear but a sawtooth: the top few bits were getting lost somewhere. Development required Eclipse, and the reboot-download-reboot cycle took several minutes. No real JTAG, only debug logging over USB. Crashes would, however, lose the log buffer, so you couldn't be quite sure where the program crashed, and all the important bits were real-time so couldn't be single-stepped. Debugging all that was extremely slow.
A hundred hours is only just under three work weeks. It's very easy to get led into a dead end that wastes that much development effort on a feature that turns out to be infeasible or a bad idea, or an intractable bug. I think I've had one of those incidents at every job, not necessarily every year but frequent enough that they're not all memorable.