Hi @its_me ----- Thank you for the follow up, it’s good to hear from you! I appreciate the update and no apology necessary 
Moving forward, since your most recent post have there been any new observations or progress made here in regard to the Samsung Galaxy S2 staying in stable communication with your core machine? Let me know.
Furthermore, I re-read through my notes on this issue as well as your previous posts to remind myself as to where we left off. Looking back over these items the bit of information that jumps out at me immediately was in regard to your network configuration, more specifically the use of the mentioned EX7000 extender:
Network is managec by a Netgear X4S router and complemented by an EX7000 extender. Rock is wired to the extender, so are the NAS and the Sonore network player.
By chance, during your troubleshooting have you tried testing your setup with the mentioned audio components (NUC, NAS, and Sonore network player) mounted directly to the Netgear X4S router? I think it would be unwise at this time to “point the finger” at the extender but the reason I ask is because we have seen some issues pop up in the past when extenders are mixed into the chain of communication. Which is why we always recommend the use of a “true” mesh based network.
-Eric