With these symptoms, the backlights are suspect though I haven’t encountered this exact model before. The failures were intermittent so it was a bit tricky to find the source of the problem. With the TV apart, my LED tester got all strips to light though one strip measured a bit higher voltage than the others. With the TV powered up, I observed the suspected bad strip fail first before all the backlights shut down. Testing the strip, I found one bad LED (replaced with 6V) and the connector between the left and right strips was broken causing an intermittent connection.
With the TV together, I turned down the backlight level to 50 and also turned off the Dynalight feature.