When do the lift and drag vectors contribute a force component along a glider's path of travel as seen from the ground?
In thermals.

More precisely: Every time when the updraft strength increases. The glider will continue on its original path due to inertia while the airflow will have a positive angle when referenced to the path of travel. Now the aerodynamic force will point slightly forward and accelerate the glider.

Experienced pilots use this by pulling more than 1 g when flying into a thermal and less when updraft strength decreases. This helps them to gain some more energy from the rising air.

Drag is per definition the part of aerodynamic forces parallel to the flow direction, so for drag the answer is: Always. With changes in vertical airspeed, the drag component parallel to the direction of movement will merely change with the cosine of the angle between the aerodynamic and the kinetic coordinate systems.

If you insist on excluding changes in vertical air speed, your question will have no answer regarding lift.