I usually try the followings in this sequence until reconnect: (1) disable and re-enable Bluetooth from the phone, (2) disconnect and reconnect the phone from the infotainment screen (settings->devices), (3) re-pair phone (delete from both phone and car and then pair them again), (4) reset...
Firmware NA 55.00.753A appears to have changes for Pandora. Not sure what version you have, but perhaps upgrading to that version would be a first step?
This appears to be an old post, but perhaps some of you could help. I just purchased a 2016 CX-5 Touring 2 weeks ago, and I am experiencing the same issue (sudden and frequent lost of bluetooth connection). Wonder if anyone ever resolved the problem and whether anyone could share more on your...