Maybe the doors are locked. That once happened to me then i figured out that the doors were locked so try that otherwise i dont know what you can do.
Do you mean the Sim's house, or the lot where the workplace is found?
Because, if you mean house, yes that a possibility, but then the sim would wave it's arm in the air, saying somethings in the way.
But, it happened to me the first time when my sim was playing for tips near the Diner, she couldn't go to work.
So, this specific problem where the icon just disappears, would not occur with locked doors to blame.