Hello @FabioD, I’ve merged your two posts - no need to post twice.
I don’t know why you think you are seeing a buffer underrun; skipping to the next track is usually an indication of something wrong with the incoming stream. Some more information is needed and I’ve also moved your post to a #support thread so that Roon’s @support team can get involved.
In order for them to better assist you, please provide a brief description of your current setup using this link as a guide.
Make sure to describe your network configuration/topology, including any networking hardware currently in use, so they can have a clear understanding of how your devices are communicating.