Got some advice from avforums so hopefully this will fix it.
HDMI AUTO DETECT TOGGLE
The HDMI Auto Detect feature can be turned off on Samsung 2016/2017 TVs using the remote control by pressing a certain key sequence (either IR or Bluetooth remote works).
1. Make sure TV is updated to latest firmware version
2. Switch TV to TV source – HDMI may not work with BT Smart remotes. TV source works with either remote
3. Using IR Remote: Mute + 7 + 2 + 9 + Exit
4. Using Smart Control: Mute + Vol Down + Ch Down + Mute
PLEASE NOTE: TV does not display any messages after you press the above key combination. This function is a toggle. So if you want to turn HDMI Auto Detect on again, press the same key sequence.