Sony XDCAM footage from EX-3 imports into FCP X 10.7, but the sound cuts off

Hi. I'm importing Sony EX-3 footage into Final Cut X v 10.7. Some of the files have imported with no issue. FCP doesn't have any issue recognizing the Sony cards. However, on some of the longer imports (2-3 hours), all of the video imports fine, but the audio cuts off at some point. Just silence. No waveform. Sony's Catalyst Prepare appears to make files with no issue, but that is a subscription, and using FCP directly is much more convenient. Any idea why this would happen? It does so consistently. I have an old Mac Pro with FCP 7 that loads these files fine with Sony's XDCAM importing software. Again, FCP X directly would be much more convenient. Thanks.