Audio missing in iMovie when importing screen recorded video
I stole this question and edited it to reflect my situation, because I found a simple solution but was unable to comment on the question.
The solution is Quicktime > File > Export As > Audio Only...
Then just drag the audio file into iMovie and make sure it's lined up with the video that was missing audio. I'm not sure if this negatively affects the audio in any way, so if this is for a professional project, you might want to export the audio using something that doesn't compress it or whatever. It worked very well for my purposes!