I have a good micro SD card and recently upgraded to a RP 4. Despite that Rune is running like maple syrup on a cold winter morning. I end up staring at the flashing "Rune Audio" screen for long periods of time up to and including forever. I can't imagine everyone is having this issue or it would be the number one thing people were talking about. I started with a formatted micro SD card and used the DIY build instructions. Everything went fine, but its a real dog to set up due to the extreme slowness.
I used a pre-built image last night at 11:00 PM and told it to scan my nfs music share. It is now 9:20 AM the following morning and it's not done. Raspberry PI 3B+, latest Rune Audio, 5 Ghz WiFi connection.