Qobuz stops playing via Roon.

Running on what is what I was looking for mostly. 
can you enable another device as end point and try to stream to it and see if same issues persist? This could be your ipad or phone. 
if that works then there's something with your device settings for the Lumin in Roon or in Lumin settings (Lumin app). Could be your wifi is weak if core is not wired. 

Oh sorry.  HP laptop with a 1TB hard-drive. My iPad and phone work just fine as a remote.  I do have a Wi-Fi extender for the LUMIN so do you think I should try to connect to it instead of the router? 

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.