I am having the same issue. Searching is very slow. I also have dropouts when playing. The dropouts seem to occur more often using Roon Radio than when playing an album
Setup:
Core: Synology DS916
Remote: iPad Pro 2017 and iPhone 8
Streaming device: Linn Majik DSM (2017) LAN connected to Core
It seems to be getting worse after the most recent update (Roon 1.6 (Build 401))
So we can better assist you, please describe your network configuration/topology, including any networking hardware currently in use, so we can have a clear understanding of how your devices are communicating.
Is your Roon database stored on an SSD? How many tracks are in your library?
Can you confirm what kind of CPU the Synology Core is using?
Your Core machine doesn’t quite meet our recommendations. Do you have another machine you could try using as your Core and see if there’s any improvement?