You probably have already thought about these things, but:
* Audit your playbook. See which plays are resulting in interceptions and see which defenses your opponents are in.
* Self-scout. See if you have become predictable out of a certain personnel set, or in a certain field position. You don't want to be easy to scout.
* If it is Scales you are referring to, his passing accuracy is only 73. Considering that, his career numbers up to this season have actually been pretty good.
* Play familiarity helps, but there are also defenses against which you will never build up play familiarity. I think that is a glitch in the game that has been called out in the forums several times, but to no avail.