Fabian, from the Delight team, says:
The old Nokia drivers are made for XP, Vista and 7 and not compatible with Windows 8 or Windows 10, the driver signature isn't valid/compatible anymore. It also seems that Nokia didn't use proper/offical APIs back in the day.
However, Huawai uses the same common/BB5 APIs and their drivers are compatible with our devices and with Windows 10.
So the workaround seems to be (somewhat bizarrely) to use Huawei's drivers to let Symbian smartphones still sync!