Roku Streaming Stick 4K 2021 connected to Samsung 50" - TU700D Series - 4K UHD LED LCD TV (Costco)
Periodically, when turning on Roku/TV, Roku displays a 'black screen' and following by Samsung saying "HMDI Device Not Connected".
Re-booting the Roku fixes this obviously. I also discovered IF you switch (using Samsung remote) the source FROM Roku TO Another Source (Antenna) and then back to Roku, the Roku main screen will appear quickly as normal (device did not reboot).
Notes: (1) Using Roku to power on TV/Roku, (2) have set Roku to be constant ON via options menu (doesn't appear to have any effect).
What you are seeing is entirely normal. Happens to me. Your Roku is going to sleep. So when you turn on your TV there is a "no signal message". Pressing the home button wakes it up. If you do not want this to happen then disable the bandwidth saver. Some devices also have a a power savings feature you can disable. But it is entirely normal. Also be sure you have your Roku plugged into the wall outlet and not USB TV power. There is no "constant on" option. A Roku never turns off. Just goes to sleep.