Audio Drops out completely when I export to MP4

Since I upgraded to 15.2.0 I have had serious problems with the audio cutting out when I export to mp4. It just cuts out randomly and never comes back. When I look at the sound wave form it suddenly goes silent. I have had this really bite me because I didn't expect it in my workflow and suddenly had a video with no sound right before I was going into a show. 

Now my only fix is to export to prorez 442 and then convert using Hanbrake. Encoder also leaves me with no audio shortly into the video. 

Obviously this is a workaround for now, I would love to be able to depend on my audio being there on the export in the future. 

This is happening on several videos, most recently on a couple I imported after recording them in Ecamm software, which is recording at 24fps to .mov format 1080p.