Amazon Drive appears to be heavily limiting API requests today. We have reached out to them and are monitoring the situation. If you are seeing that your uploads/downloads/refresh operations are not working on Amazon Drive, this is most likely the cause.
ODrive not syncing ("Amazon Cloud Drive rate limit exceeded")
Mac Client w/ Amazon Drive not syncing (uploading) new files in folder
Amazon is continuing to work through this issue, but the situation has improved. I will update here when this has been fully resolved.
This should be completely resolved now, but ping us in the forum if you are still experiencing issues.