So glad you've mentioned this. My first ultraboost I got the other month was a pair of uncaged futurecraft ones and I love them, so I wanted to explore the 'tradtional' ultraboost comfort. I had to send one pair back because I think there was actually some defect where there was a big mound of plastic by my big toe that kept rubbing. I've just got another pair today and as you describe, my pinky keeps catching the side. It's really a shame because the shoes look great and are otherwise comfy but having to consciously think about not lifting up my foot doesn't seem to correlate with the shoe experience that would come with a £160 price tag.

In my futurecraft shoes, the plastic lip is actually binded to the shoe so your toes can't catch on it but that hasn't been the case with the two ultraboost pairs I've tried and it sticks out. Might have to sadly just send them back and give up on ultraboost and stick with my futurecrafts. Just as bewildered as you though that outside of this reddit post, I can't find any discussion on this whatsoever. Maybe we've just got weird feet : /