Welcome to the community, @Stefan_Hahn. I’ve moved your post into its own topic so that Support can respond to it.
Can you please fill out the details shown below so that they can better assist you? Thanks!
Roon Core Machine
What version and build number of the Roon Core is your NUC using? (version 1.0 build 227 is the Roon Operating System, not the Roon Core application) Roon Remote
What version and build number of the Roon Remote is your Samsung tablet using? Networking Gear & Setup Details
Your network gear (model of routers/switches) and if on WiFi/Ethernet
The network address of your Roon Core, and the network address of your Samsung iPad
Tell Support about the problem you’re having in as much detail as possible. Screenshots are always appreciated!