One of the more frustrating ones for me was the additional missions for the Millennium Falcon ride. The original plan was to open the ride in 2019 with multiple missions and they got very close to finishing some of the others when the ride was being built and tested, but they got cut at the last minute for budget. Now we have to wait until 2026.
I know that it’s a lot of work to design and test what’s essentially a new level for an existing video game but as a mechanical engineer I can’t help having the mindset “what’s taking so long?? It’s just software! The machine is already built!”