I won't say much publicly, but if this is the issue I think it is (customer has a huge number of files, and is trying to sync it with a 32-bit client, and hitting memory issues), we are aware of the issue, and are definitely working on it.
It's a tricky thing to solve in any sync client - for example, Dropbox has a cap around 300,000 files (I believe this customer had 700,000 files?):
> https://www.dropbox.com/help/space/file-storage-limit
Note: The performance of the Dropbox application may start to decline when you store above 300,000 files.
Other clients may have similar limits. I'll see if I can find our docs on it.
Disclaimer: I work for Google.