Hi,
My Sim disappeared too,but not when traveling-this is what happened. I have WA and Ambitions. I had a couple (Bill & Ted) who I decided to split up. I sent Ted off on his own and left Bill as the main character so that I could develop it further. Ted's house shows up on the map, as does Bills. But Bills picture has gone from the usual place in the start up screen. And when I go to play the Bill character all I get is the big map view and the house doesn't load. Even though I made Bill's house the main character for game play. This never happened when I had WA only. So yes I think you're right there is a glitch somewhere.