For what it's worth, my single right channel pop incident was unrelated to the optical connection. I can't recall whether I was streaming (Spotify) or playing from a USB stick when it happened but it was one of those. As I said, probably not enough info to connect it to Paul's issue but, if it happens again, I'll update here.
Well, I still have my Atom connected to my TV through HDMI, and the sound dropoff issues is still there. However, my speakers are still working really well, no fried tweeter nor other damages to my speakers.
I don't believe it has something to do with the volume: i listen to my music at really loud levels and nothing happens when listening to music only, until switching to TV. Then, the issue will appear every 2 hours or so and no matter whether the volume is high, medium or low.
I second all the comments regarding the Atom's superb sound and abilities to draw you into the music, it's by far the best piece of kit i ever owned. I only feel great frustration that the unit is that unstable and buggy when you connnect it to a tv set.
I don't have any Tidal account so can't comment on the unit's reliability when streaming from those streaming platform.
I can confirm though that the app has really serious issues to find the device, get it connected to my Synology NAS.... setting up precisely the volume using the app is a real nightmare; e.g. you will think sliding the volume bar but you actually pressed on pause, sometimes there is a lag between the app and the device's response.
To me, the app is the only one to blame for all the above. But when it comes to the annoying sound-drop offs the speakers when watching tv, this to me is the most critical issue. I'm trying to be optimistic reminding myself that it only happens when the source is TV, hoping that Naim will solve it.
I'm both happy (the Atom's gorgeous sound is second to none of the hi-fi kit i've ever owned, and I owned quite a few) and frustrated (this buggy app makes me mad !!!)