Audio sync issues in FCP X

Here is the scenario: The video shoot is an interview format. I recorded my audio externally using the Zoom H6. The sample rate was set at 48kHz, 24bit.

The camera used to shoot the video was a Canon 60D. It appears that it recorded its audio from the internal mic on the cam at 48kHz. The frame rate was set to 1920x1080 @ 24fps.

I bring the audio and video file into my project on FCP X and sync them to my slate. Slowly but surely the external audio starts to fall behind the video.

Project settings for FCP X are: 1920x1080 | 24fps. Audio is Stereo | 48kHz.

Please help! What am I doing wrong here?