I've had the same issue with JRemote for IOS. Was working OK from outside my network for years but suddenly last year stopped working without anything having changed in my setup (same Iphone, same desktop, same modem/router, same ISP). Did all the usual checks to ensure port-forwarding set up OK and testing outside access working OK by clicking on the Access Key in Media Network settings. Everything set up fine but when I try and connect via JRemote I get the following: 'Connecting to IP xxx.xxx.xxx.xxx, Response recieved, Name of server is xxxxx, Authenticating with credentials, Could not connect (network is unreachable)'.
It works fine when connecting from outside my network via Panel - it's only JRemote that has the problem.
The only thing I can think is there is some issue with the way JRemote/MC handle the username and password credentials when connecting via JRemote. With Panel it prompts for the username and password after connecting - but JRemote somehow sends the stored username and password at the time of connection.
Perhaps this is an ISP issue? Maybe the ISP have somehow tightened up on security by preventing the use of stored usernames and password credentials when allowing connections from outside the network? But just guessing here...