Same situation here, with images sometimes not loading, and constant “An audio file is loading slowly…” errors.
Roon Core 1.5
iMac 27", os 10.14.2
Synology 1600 router, ROCK and Mac on LAN not wifi
NUC i7, 8GB, 256GB SSD (fast one), 6 TB RAID
Works for a few minutes, then get worse and worse whether Tidal or library. Restarting everything restores function, briefly, then it quickly degrades.