I installed OpenElec, then upgraded it to LibreElec 7.0.2, and then downgraded it with the CvH DVB Drivers edition to 7.0.1 (I'm sure there's probably an easier way of doing this, but I'm learning as I go along!)
Once I install the TVHeadend 4.2 version, and access it using the default login, I switch to the Configuration -> DVB Tuners screen, and it shows just "TV Adaptors", no adaptor.
I've spotted there's another thread (LibreELEC) which mentions this similar event, in which they were asked to provide some pastes of logs, so here they are:
This is a Raspberry Pi 3, and the adaptor is a Tevii S662 device.
Hope you can help!!