Captivate 2019 - Published video: sound quiet for the first 2 minutes

Personally I always replace the original audio in the recorded Video Demo by a more polished one, because I find it very difficult to focus both on correct Video capturing and good audio. Did you try that? Moreover try not to capture too long videos in one capturing process, but split up in smaller chunks. That would allow to detect the problem more quickly. Those are some of the tips I summarized here:

https://blog.lilybiri.com/video-demo-tips

Have you verified that this video plays the same regardless of the computer on which it is played? 

If it turns out the issue IS with low volume video recorded on the video, you should be able to separate the audio from the video track with an editing program and then increase the volume of the affected audio to rectify the problem.

If the video is simply too bad to fix, re-record the video and see whether the issue reoccurs.  If it does, there would appear to be something wrong with your recording hardware or drivers.