Similar experience happened to us in Hamburg airport. 25 years traveling around the world, never seen a transit passengers being searched thoroughly to go to their connecting flights. And slow german out of date machines and security system. Never ever go to Germany again.
My wife and I were on a tight connection schedule on August 11, 2019 at Terminal Z at FRA. We were confronted with some 300 people in the line for security. Our arriving flight was late so we had only minutes. Most airports will accommodate those who are late, sending them to the front of the line. Not at FRA. The woman in charge of the line refused, claiming "You'll be okay." She lied. Two others I know missed their flights because of this woman's mendacious statements. With some 50 people still i front of us we jumped the line and made our connecting flight to IAD just as the gate agents were preparing to shut the gate door. It didn't help that security needed to put my bottles of olive oil, sealed in airport security bags, through some examination machine. What is the point of the security bags, then? Overall, I will try by whatever means to avoid FRA in my future travels, and will urge my friends to do the same.
Sometimes you are asked to get off the airplane on the tarmac and take a bus to the airport add to that the security check .
If you have a connection flight you may miss the flight , i had to run to be in my other flight because in addition to the previous reasons a had to go from one side of the airport to the other .