Sounds like a known issue with the latest Samsung firmware, certainly in the EU anyway. Samsung are working on a fix, but the workaround is:

Settings, Broadcasting, Turn off Autotuning.

This seems to have resolved all my black screen issues.

Dupe...

Just re-read your OP, you issue does sound slightly different, but maybe related so probably worth a try. We are mainly seeing issues after the TV has been off for several hours and displays a black screen once turned back on.