Why does condensation appear on surface of window, but not all of them?
Condensation is all about the dew point which is determined by the relative humidity along with temperature at the surface of the window. Although RH is probably consistent across all of the panes, temperature will vary due to air circulation or convection. This could cause one pane to gather condensation and the one next to it to be dry.
This isn't an issue if the condensation is on the exposed surface of the window. If they are double or triple paned and the moisture is between the panes it would indicate a leak in the seal which results in lowered efficiency.