For what it is worth....
In every case so far, where this has occured with clients of mine.. (and where it wasn't related to the stall issue and certain network conditions.. which was fixed in 10.0.1) the issue has been found to be caused by either..
Their ISP and Max File size limits..and/or intermittant internet/WAN routing issues, (The most common cause)
Their own LAN network and it's related equipment such as rounters/firewalls/other apps installed and running in the background.. etc.. such as Little Snitch..(Fairly common..)
In one case... Energy settings on the Mac... putting HDs to sleep for example..
and in another it was related to a permissions issue and a HD that had some errors on it...
Finally I found a few were caused by deliberate or accidental stopping of the downloads initially which leave corrupted or incorrect data on the HD.. (Fixed by doing a full uninstall of all previous content downloaded)
If it was a general bug in Logic Pro X then it would affect a much larger number of people than it does...
That's not to say it couldn't be related to buggy code in Logic to download the content.. as anything is possible.. but again, in every case i have handled so far for my clients.. (apart from the stall issue which was fixed) I have found it was something unrelated to Logic Pro X itself.. . and those very same clients, when it was applicable, had similar issues with Logic Pro 9 and it's additional content downloads..