When turned on, the backlights flash and the front led flashes a one blink code. According to the service manual that can be found online, it is a backlight error.

I recorded a video of the flash and from a still frame, the third row was not lighting up. The left and right strips did not come on and I found two bad LEDs on the left strip. The right strip tested fine. This TV has local dimming and though left and right strips are wired separately, they are dimmed row by row. I used Samsung 3V LEDs and the color was a bit off and they were a bit brighter.

I decided to take apart the TV a second time to move the repaired strip to the bottom of the TV and also remove a fleck of dirt trapped under the panel. Unfortunately, I cracked the panel after putting pressure on the edge when I missed a screw in the bezel. In hindsight, I should have removed the bezel completely with the TV lying flat.

For the record, part number for the strips are as follows
Left CX-60S02E01-3B5Y3-0-B-523-1208-U
Right CX-60S02E02-3B5Y3-0-B-523-1297-U