This bug was fixed in a recent title update. You should now be able to create custom playbooks which contain formations in the 3-3-5 set. Formations in the 4-2-5 set show up in custom defensive playbooks with the "Big Nickel" label.
The bug fix which allows 3-3-5 in custom playbooks does
not apply to any custom playbooks you created before the title update went live (so basically any custom playbook created during the first two weeks the game was available to the public from Monday deluxe edition unlocking onward), nor does it apply to any new playbook you create with an older (bugged) custom playbook as a base. You have to create a brand-new defensive playbook from one of the base playbooks provided by EA Sports to get the fix.
If you're still having issues, please discuss in the
EA CFB 25 Custom Playbook Thread.
Closed.