Unsure where the lag stems from - whether from BluOS, Deezer app, or AirPlay. What I can say, is that this issue was experienced within my similar configuration approximately 1.5 years ago regardless of the multiple BluOS updates and hardware (Node then to NAD).
In respect to AirPlay, I’ve preferred Connect features via Spotify or Tidal. Primary reason is because my phone’s battery would be drained quicker than usual with AirPlay. I also felt, and someone correct me with this notion, that with Connect you’re not streaming from your phone, but instead using your phone (or tablet) as a simple remote for the Node which is actually doing the streaming instead of your phone with AirPlay. Within the Connect framework, I would presume it would be a better/simpler stream vs phone>streamer>preamp/amp>speakers via AirPlay, even if using Deezer FLAC which may be better than non-MQA Tidal. These are big assumptions on my part, though!