Engine Prime is continuously accessing the file system and the database in the main UI thread, causing the rendering loop to freeze and the OS detecting the application as frozen.
On plain English, the program is written in such a way that every time it needs to do a heavy operation accessing the files in the disk, the UI will freeze and it will be unresponsive, although it’s actually doing wrong.
The programming of Engine Prime is simply bad. I’m sorry to say this, but it objectively is, and the proof is that we are experiencing what you describe when importing big folders into the collection.
In my case it took about 15h to progress from the “creating playlist” operation, which completely froze the app.
I waited for a ridiculous amount of time and it eventually worked.