After compositing , the 3d model gets faint and translucent in the final render i was following the CGGeeks VFX trick shots , i had downloaded the assets and was making the trick shot , but the problem appeared in the last step , COMPOSITING , after compositing , the fake ball get faint and translucent (is this property called alpha?) , how to fix this

as you can see the ball is very faint in the sky
looks like i was not key-framing the factor node in the compositing properly , the factor was increasing from 0 to 1 in 70 frames but it was supposed to remain 1 during those frames