I have the same issue in Roon 1.2 on a Mac Mini with similar specifications as Chanjin_Shin. The issue is experienced on two different USB audio devices, on different high-end Macs. The hiccups occur quite frequently, every minute or so, sometimes just seconds apart. Storage is probably not the issue, it happens when playing from my NAS, from TIDAL and from a local SSD.
Playback is uninterrupted when I use other software, Decibel for example. (Available on http://sbooth.org)
I would suggest making a new thread under support describing your situation and providing all details about your setup. Maybe @andybob can help you get started by splitting this into its own thread.
For Chanjin, his issue was indeed resolved as he discovered what was causing his extraneous network interference. Even though you are having similar symptoms that does not mean that the issues or fixes are the same. Which is why you should start your own thread.
Roon Core is on the Mac Mini. Playback issue occurs on this machine too, as well as on the MacBook Pro.
Network is wired, gigabit CAT7 cables with a gigabit fiber to the home connection. There are two gigabit switches between the Mac Mini and the MacBook Pro (ethernet over Thunderbolt), three between the Mac Mini and the NAS.
Devices are PHIREE U2S and ASUS Xonar Essence One.
Note that the issue wasn’t exclusive to playback of files over the network, also files on a local SSD were affected.