Mate I'm no expert but if you rewind and pause the match before your CB gets tackled -
Does he have a couple of options to pass to, like if it's the LCB does he have a clear line to pass to say the DL/WBL or his CB partner or the DMC?
If he does and he isn't passing to them is his passing set to low? maybe it's too short so he wont pass?
Is his creative freedom set too low? I found when it was too low they became zombie like.
Is his mentality set too high? I found when I had it set high they got too brave with the ball and fronted up opposition players only to turn to the side not pass and get tackled.
When the DC's get the ball do the DL/DR run foward straight away? Maybe they need looking at?
Are too many players running from deep and taking up advanced posistions too early? Maybe they need to be looked at?
Like I said I'm no expert just a few things I had to look at when I had this problem.