I have just had new equipment and suffering the same black screens. Changed everything cable wise but re booting the TV box solves the issue. Sadly it took 4 days to find this out and why I didn't do it before I don't know.
Sadly yes after re booting the TV box the issue returned. I had to call 150 today to report it as it wasn't the TV or canbles. I explained to the call center agent and he told me to re start again and whatever he did, well its solved my issue for now but I am sat in anticipation its going to return.