Thank you! Good work around, I am syncing with the client now to a temporary library.
You may be on to something here, as when I take a closer look at the logs, both the cloud file browser and the android client use POST to seafhttp/upload-api in order to upload their files.
I am experiencing the same frustration with the android client in my other forum post that has me pushing the developers sort of hard to get this resolved - unexplained upload failures when there's a large amount of files queued up in the upload queue.
I bet an underlying weakness with the way the upload api works that both the cloud file browser and android app utilize is the cause of these issues.