Rpi3 volume levels wild auto-adjust

As of about a month ago, playback of all video files under osmc on the rpi3 started exhibiting dramatic volume shifts during video playback. I’ve tried several know good h.264/mkv and mp4 files. Generally, it sounds as though an algorithm reduces volume during quiet sections of the video, and then raises it up again once the video gets into a section with louder audio. This is sometimes, but not always. I allow osmc to auto install updates (apt-get update) , but not quite sure which one caused the issue.
Is this a known issue? any workaround?

You need to enable boost center channel on downmix when you are viewing media that contains a 5.1 audio track on a 2.0 system.