The behavior you describe is standard. Few international trips clear when you request the upgrade, unless you pre-selected the flight to have upgrade space ("R" class) already available before you purchase. The C class seat map appears, but is not selectable, when you request the upgradeand are waitisted. It's useless if and until the upgrade clears. And for a Silver member, it will be worse than just waiting until 24 hours out. On SFO-FRA, it is not likely to clear until just before they close the aircraft door, and, frankly, for Silver, unfortunately not likely to clear at all.