SDD Replacement

[DeltaMikeCharlie]

Have you tried: 1) Powering-off the IceBox; 2) Changing to the other HDMI port on the IceBox; 3) Making sure that the TV is on, and; 4) Powering-on the IceBox again?

LibreELEC (the underlying OS) should select the HDMI port with has an active EDID.

Also, does the line show on the splash screen as the IceBox boots?

Next step could be an RMA.

[NBOSTI]

All good advice given.
You have said that your TV had a software update recently, and that was when the issue started.
Depending on the brand of the TV that could be the problem.
I have Samsung TV and it likes to hijack things at times, set preferences to what it believes to be best, particularly devices connected to HDMI ports.
Most brands of TV should have a similar interface, but with the Samsung I go into the "Sources" menu and edit each connection there. Icon, type of device etc and if none are preset I choose "other".
For my IceBox I have it set as a PC input, which essentially it is.
If I unplug all HDMI devices , turn the TV off then on again and replug devices the Samsung goes into it's routine of "helping" me set them up, including configuring the TV remote as universal to operate all. I don't like that, so I configure manually.
If your TV has a dedicated labelled HDMI port for PC try using that.
It all sounds to me like it was the TV software update that has changed some settings, be patient and work your way through them.

And as mentioned by MD and Delta Mike Charlie, try the Icebox on a different monitor, that will help you narrow down the issue.