Expedition Technology Digital Signal Processing Engineer interview questions

First interview was with HR. The second interview was a phone screening. The third interview was about 4 hours on site, which included talking with 2 people at a time as well as a technical presentation delivered by you on a technical topic of your choosing. I spent hours on the presentation and then the final interview, to then be denied on a perceived lack of a skill that should have filtered me out in the phone interview. This is the one interview process I have been through where I felt my time was unnecessarily wasted. And it was a LOT of time.