Copying clips multiple time and audio not playing in copied clips

I'm creating a video with the same clip being repeated over and over numerous times. The first few times the clip copies just fine. Towards the end of the video, the audio disappears and the clip is muted (even though it shows as fine -- everything on the timeline looks normal, except the audio disappears during playback).

To make matters stranger, when I move the silent clips up a track, the audio reappears but then the clip prior to it, which previously had sound, goes silent. 

I am hoping this is just a playback glitch and that the sound will be fine upon export. I haven't tried exporting yet as it is a very long video, and I am hoping to get some answers during editing if possible. I tend to trust that what I see in preview is what will be exported, so right now the end of my video is silent for reasons that I can't figure out.

Thank you in advance.