fast forwarding thru a show

I recorded a bunch of shows on a network during a binge feed . . . some shows I can fast forward and actually see the show as I do,other episodes the fast forward happens but you can't actually see it occuring on the screen ,how come ? The video stays fixed but you do fast forward ,when you get to the point you want ,the show did go fast forward.

If I am looking for something in the show it makes it difficult ?

Why some episodes I can ,others of the show I can't ?

al