Adding dropbox library to layer causes lambda timeout

I can't say off hand why that would be timing out, but given that it works locally it does seem like it is related to that lambda environment. I recommend referring to the support resources for the lambda environment to debug this, or to see if you can enable more verbose output at least. Unfortunately as that environment isn't made by Dropbox we can't offer specific technical support for it though. Apologies I can't be of more direct help. If you do find an issue in the Dropbox or Stone library itself of course please let me know and I will raise it with the team to see what we can do about it.