[Resolved] Why is this causing errors?

In light of recent events, I think I have found a big cause for the machine dieing.

Variables.

Though painfully obvious to those in the know, it isn't for me.

const device_name = global.get('myDeviceName');

node.warn(" Device name " + device_name);

const flow_name_ = flow.get("name");

node.warn("Flow name " + flow_name);

msg.topic ="ERROR_REPORT/" + device_name + "/" + flow_name;
return msg;

My suspicion is the const rather than let.
As the device_name and flow_name are not going to change, after reading the new stuff on how to use let and const (though it used to be var for the first one) why is it creating errors?

Ok, I've changed it from const to let and it is still creating errors: hand over fist.

Any elephants I'm missing?

ARGH!

The missing _ at the end of the name for flow_name_ in the second last line!

(I'm an idiot!)
RESOLVED!