Kevin,
The Error 14 in a nutshell means that the client cannot reach the port or see the connection to the SMP server. So as you mentioned above, the client will not be able to tell if it is network, firewall, TLS version and so forth.
So we just compiled the different checklist for Error 14.
http://service.sap.com/sap/support/notes/1814081
One of the most recent reports from the field on Error 14 is with respect to Load balancer usage wherein the Load Balancer of the customer just uses the default time out. It automatically cuts it at 5 minutes. So when the IT or security team improves the setup instead of using default, they did not see Error 14 anymore.
Hope this helps.
SAP Mobile Support Team