Audio Keeps Repeating and Skipping in iMovie

I need some help with iMovie. You see, I'm trying to edit a video in reverse, which is simple enough, you just got to press the reverse button and then, bam, your video's in reverse. The problem that I'm having is that when I reverse the video, the audio doesn't really reverse perfectly, and it kind of repeats and skips every couple of seconds; like it'll repeat the same exact audio, and the video ends up being out of sync as a result. I don't know if it's because the video I'm editing in reverse is in 1080p60, and my laptop cannot handle reversing a video that's in 60fps because it has 8GB of memory and is an Intel Macbook.

But, I've edited other videos that were 1080p60 before this, and I did not have this issue. So, I'm not sure if this is become of the new version of iMovie or what because the last 1080p60 video I reversed was before the update. I would like to know what's wrong, and what I can do to fix it, so that I can reverse this video with the audio perfectly reversed as it was when it was forward, and in-sync with the video.