It's been a while since I paid attention, but doesn't the priority security line in FRA say "First / Business / *Gold"? Or am I imagining that? If so, it obviously wouldn't help you if you're silver but certainly would for Gold / Platinum.

Agreed about passport control not being CO's fault and the gate agent being in the wrong. At passport control though, I can only imagine you've run into this issue before if it takes 30 minutes to find an individual stamp. Wouldn't you find it yourself and show it to them? Arrive at the counter with your passport open showing them the stamp in advance?

It's a pretty sensational headline though for an issue with one gate agent in one airport

Based on the OP, I assume passport control - the OP was in the front of the Y cabin.