Hi,
I use the newest BIAB 2015 Bluegrass Pak and I have exactly the same problem:

Difficulties to use the fiddle RealTracks 428 (chops and shuffles) and 430 (shuffles)! No shuffles to hear!

No. 429 with just fiddle chops works very well.

Style is: BLUGRSF.STY . The shuffles on the demo song work well!

I just wrote to the support about the problem and I am awaiting for the answer.

Mark