In the cold light of morning with the knowledge that problem was likely the build standard on a mis-shipped unit I took a closer look at the non-functioning unit and compared more closely with the previous four.
Dho! Why didnt I check earlier…
This is lable from the bad unit:
Note the device part number (not the model number which is consistent TBMH100) - TBMH100**915**xxxxx
Another clue is the FCC ID - might expect on a generic part but should have been a clue on a supposed 868Mhz EU unit.
Checking the other four they all look similar to:
Note correct device part number - TBMH100868xxxx
My error was in setting up the 1st 2 units and configuring onto TTN I looked at the label (2nd type) for the EUI # (the 58A0C…) for Console set-up and registration. I then realised that the web view on the device during set up/conf shows all the device details - inc the EUID - so for 3rd onward I just looked at web interface and copied/pasted the EUID from there into the TTN console.
That worked fine for the 1st 4 units but of course the 5th was this US build and I never got to see the label to spot the change
Lesson is - check ALL units shipped form RS Components on receipt & double check labels and build standards as you configure and deploy. Just because they came in same batch doesn’t mean they are the same device…