I had a similar issue when I first got my BC296D here in Denver....
I thought I needed to adjust the Sound Quality when programming a P25 system so I adjusted the Sound Quality and got the exact same results your having - the radio will trunk and land on talk IDs but no audio in the trunk mode. When conventional, you hear the audio.
On pages 56 and 57 of the owner's manual, you will see the settings for Sound Quality. I followed steps 1 and 2 to reset the radio back to it's default audio setting:
1) While monitoring a specific APCO P-25 talkgroup, press the HOLD/MAN key.
2) Press and hold the 9 key.
Hope this helps.