Quick update on my position; I did contact Yuneec UK about this and received a prompt reply:
"Hi Paul,
Thank you kindly for your E-mail. From the message below we believe your Flight controller or GPS module may require replacing, if you are located in the UK you are welcome to send this into us for diagnosis to confirm which one may need to be replaced. A rough estimate for repair would be £120 inc return postage but we can confirm this upon checking the machine. If you wish to go ahead for us to look into this and you are located in the UK, the address is listed below. Please include a covering letter confirming your contact details and information on the return.
Kind regards
Graham Eldridge
Customer Services"
They seem confident to be able to fix it at a modest cost, however in my case I have taken what may seem to be an extravagent solution in that I have just purchased a BNIB Typhoon H setup, has actually arrived this morning.
Briefly, I purchased my H secondhand but " New & Unused" in August 2018, unfortunately a few days after a family member committed suicide so the H was largely forgotten for several months. When I did get around to sorting it the first thing I discovered was that of the 4 battery packs it came with, 2 were U/S, individual cell voltages were as low as 1V. I've had numerous minor niggles with it plus some erratic flight behaviour, which I initially put down to my inexperience, but now with this GPS problem I've realised that it is probably a lemon and only safe thing to do is to use it for spares.