Yep, disconnecting the LAN and wireless network adapters before starting SNAP allows SNAP to work correctly. However, I lose access to the network drive containing my imagery…
I might try downgrading my JRE to something even older (I only went back to Java 1.8 build 82 before), to see if the dependencies that the SNAP Java instance uses are causing the issue.
UPDATE - keeping the existing version of Java, but disabling proxy access by setting ‘No Proxy’ in the ‘WWW’ options in SNAP allows SNAP to continue working, and to access the network over the LAN. It’s an interim fix, but it prevents the user interacting directly with the interweb through SNAP.