In the unix.xml file, you will see that each OS command has a flag called "RepeatingCommand". For the GetTNSAdmin query, this flag is set to F (False), which means it will run in the static SSH connection. It is well worth trying changing this flag just on this query to be "T". This will force it to open its own connection to run the command and then it may well return data more successfully than via the static connection it is currently using.
A minor bug. As this does not happen all customers.