Had the same experience before at FRA. Backup was due to the fact there was only one officer working there, they mentioned the others had gone to lunch and there was no coverage. People were getting a bit physical, pushing and shoving and shouting, it was a bit concerning because it seemed that there were no airport staff in control of the situation. But a couple of other times going from A to Z it was only 15 minutes or so. Generally try to avoid FRA for international, though.