The first rounds you were going for new graduate positions, they were looking at your side projects because juniors don't have anything to show, and they saw so

The first rounds you were going for new graduate positions, they were looking at your side projects because juniors don't have anything to show, and they saw something in yourself, a cheap youngster willing to work hard probably like they were at your age. (You're right that 27s was not fresh out of university but it was 20s nonetheless and you were treated as a junior / new graduate) The later rounds you are going for experienced positions, they have much higher expectations. They want to see successful experiences at previous companies, building things (preferably the same thing they are doing), working with coworkers, delivering in a more-or-less corporate environment. It's completely different expectations. A side project is out of touch at best.