The issue is now fixed. The root cause was an outage in the US-EAST AWS S3 service and more details are available here: http://status.aws.amazon.com.
Posted Sep 14, 2017 - 20:06 UTC
Monitoring
A fix has been implemented and we are monitoring the results.
Posted Sep 14, 2017 - 19:55 UTC
Identified
We have been experiencing errors with uploading attachments and avatars due to an issue with our downstream service provider. We are closely monitoring the situation.