The network board is pretty similar in all current dCS products that feature it. So the problem that you have would likely be well known if related to the board as it would affect owners of Network Bridge, Bartok, Rossini and Vivaldi. But , insofar as this forum is concerned, I know of only two people reporting it, both Bartok owners, yourself and Robertt though identifying the source of his problem seems to me to be complicated by his need to use the text to voice translator on his i-pad to navigate Mosaic.
So there may be two rogue network boards out there or the problem may not be related to it at all but to the network which I know that you have tried to isolate as its source . However reading the whole thread I still think this may be a network problem. Why? When you used Roon and it all worked OK Roon was not using the wired connection but was “airplay streaming” i.e. using Apple’s answer to Blue Tooth. Lossless but limited to 16/44.1. You then say :
But if you were airplay streaming you were not actually using the cable. So this too suggests that it may be that it is a network problem, perhaps wholly or partially related to the wi-fi. Have you checked its signal strength?
If it is not a network problem then that seems to leave the possibility of a faulty network board as I think everything else has been tried by you . If so it cannot be solved here. You would need to involve your dealer whom you do not appear to have much faith in from your remark above.
In the UK I would pick up the phone to customer services at the dCS factory at this point just to ask if they had any experience of this problem. Is that possible with dCS Americas?
Incidentally I once had a problem running Qobuz on a a PC where it kept dropping out.I was convinced it was Qobuz’ fault. The solution? Changing the port I was using on the router. It seems that not all ports may be equal.
Finally, before involving your dealer or dCS have you a friend who uses streaming? Could you take your Bartok to him/her to try it out to see if the network connectivity problem recurs in their setup?