I have a 5K iMac from 2014 and since the update to Sierra I've been having intermittent internet issues. Maybe once every 2 hours the blue progress bar in Safari will just stick about a quarter of the way through, for up to 15 minutes, and then will just load like nothing happened. All other internet based apps, Apple Music in iTunes etc, are also affected. All my other devices are unaffected when this happens suggesting the internet connection/router (AirPort Extreme) is operating normally. I've tried a hardware test which came back without issue, deleted Network preferences and I have reinstalled Sierra from recovery utilities, and the issue still remains as intermittent as before. The only thing I haven't tried yet is a full clean install, but obviously this would be a last resort. Has anyone faced a similar issue and got it resolved?