I’m experiencing very similar issues. Roon core is exclusively running on an iMac mini with a hard wired interconnection. I assume HW and/or internet connection is not the bottle neck in my system.
Once a HiRes song has successfully started and running and I jump then to another song from the same album the system hang’s. While leaving it in this stage waiting for the music it can happen that the song starts after a couple of minutes. This let me think that the complete album is getting downloaded before you can play it.