I think you have a different issue. The people in this thread have the issue that the downloading is simply slow, but once the files are downloaded, it works.
If I interpret your many posts in various threads correctly, you seem to be having the issue that the downloaded files are corrupt / cannot be played. This happened to several people when ARC was new, me included. However, several people reported that this seems to have been fixed, and that’s my experience as well. It does require deleting and re-downloading them, though. I did this before Christmas and so far my 30 GB newly downloaded files have all played fine, as far as I tried them.
This was also stated here by Roon support in one of your threads. I don’t know if after this you tried again with fresh downloads, as you didn’t answer anything:
If it still happens with fresh downloads, it is best if you open a new support thread and answer the questions. Complaints about ARC scattered across lots of arbitrary threads won’t get it fixed