Casting shadow on 3D text

Set the 100% white shadow catcher solid so accepts lights is off, accepts shadows is on, duplicate the extruded text layer, set the duplicate to cast shadows only, Here's a comp with everything shown that is modified. BTW the C4D renderer is a better choice but the setup for Ray Traced is the same.

Now duplicate that comp in the project panel. Drop both comps in your Main Comp and open up both nested comps. Turn off the temp background in both layers, on the top comp (Comp 1) turn off the shadow catcher, on the bottom comp turn off the extruded text, set the top comp as an inverted Alpha track matte for the shadow catcher, then turn the layer back on, set the blend mode to Multiply and add your background.

If you did need to animate the camera in the main comp you'll have to add another camera, then tie its movement to both cameras in the nested comps using expressions. You can do this by arranging your workspace as shown then just using the pickwhip to the camera in the main comp.

That should solve your problem.

Personally, I would have converted the camera move, lights and text layer to a C4D comp, done my extruding and shadow catcher there, then use C4D Lite and Cineware to do the final composite. You have about 1000 X more control of the look of your 3D text and shadows.