Thank You!
My problem exactly.
I changed the installer’s cable for one of my own shielded CAT7 cables - and hey presto the system works as is should - first time in it’s 12 month life.
We live in rural north Yorkshire (Dales) and hence have our share of power outages. It would cover the power cut but would disconnect when the grid came back - knocking off router and home assistant, a real pain recently with six or seven reconnections after a six hour outage.