Qobuz stops playing via Roon.

I was wondering if you enable your iPad as a roon end point it can be both the remote and end point (player). Try it that way. Then try Lumin native app and see if it also cuts out. May be you have a faulty Ethernet cable connected to Lumin?
I would also reboot all devices. Unplug wait for 20secs then plug it in. Do this with router, extenders, lumin

Also I should add that I rebooted laptop, router, LUMIN and iPad.  Started working better but then each song would stop about 75% into each track. Haven't screwed with it since.  I'm going to give it a little more time and if not better Roon is toast. Sick of messing with it and should be a more robust or simpler software in my opinion.  

Sounds like your network is a problem here. Do the speed test. Make sure your laptop running Core is hardwired to your router. Roon is pretty solid from network standpoint and should work fine. I run mine on mac mini with Lumin U1 Mini as end point via eero mesh and no issues to report here. 

Laptop isn't hardwired to the router. Maybe I should download the Roon software to the desktop which is but it's in a bedroom that's just off the listening area. Thanks in advance for your help :)

I had the same problem.  It was really frustrating having moved completely to streaming and never knew if / when I could enjoy my system.  Ended up buying a Small Green Computer -sonicTransporter i5 which took care of all my streaming issues.  During the process I moved my entire music collection from my NAS to an SSD internal to the i5.  It cost a little money but I could not be happier.  Andrew Gillis from SMG was also very responsive and great to work with.