Sounds like you've covered the ususal bases... haven't got a clue, -- assuming they are in fact Spotlights, and not them-thar evil, sneaky, behind your back, shadowcam-auto-readjusting Omni lights.

Skipping right over all of the DOOH! basics, (like is the Light actually on & is the Light's Shadow (opacity) dial and map size set above 0.0, etc.), so, if no one ID's the problem, you might post a screen grab of the light's dials, the view from the shadowcam AFTER the render, and the render.