Huzzah!! Unbelievably GoSolr got back to me via a 3rd party engineer. He confirmed that this is an issue with the 5kw inverters. He first tinkered with some of the settings (all remote), but to no avail. He then contacted GoSolr for a remote firmware update, which took about 30 mins. The inverter rebooted automatically, and the new option was available. I ticked the box, the alarm sounded, the inverter rebooted... Booyah! Whizzz gone!
Thanks to all on this group for the moral support through this dark and lonely road.... 😉