Continuous GPS-2 (glitch) errors when using dual GPS

Having just added a second GPS (M8N) to my Taro680PRO, I seem to be receiving nearly continuous GPS-2 glitch errors. This is only evident by the constant beeping tones while flying, and looking at the log; the copter seems to fly fine.

Is this behaviour expected when using dual GPSs? Both seem to have plenty of satellites, HDOP on the original GPS gets a little high on the attached log, but the errors are present from before then.

Log is too large to attach, here is a Dropbox link,