I've had this issue ever since I've had the mibox, however it's become more bothersome since I find myself watching YouTube more often. The audio just completely drops out for a few seconds and then comes back. The strange thing is that if I rewind the video the audio will drop out at the exact same places. Any suggestions?
Try Smart YouTube TV ( https://smartyoutubetv.github.io/ ) or YouTube plugin in Kodi. If you still get the same audio problem, it probably has something to do with your audio setup (e.g. TV settings or speaker setup). Otherwise, it's just an issue of official YT app.
Smart YouTube TV allows you to switch audio codec (opus/mp4a/vorbis) in playback options. Try that too and see if that helps.