Troubleshooting LED strip

I have (2) 4m rolls of 5v WS2812B's (60/m) from Ray Wu.

One roll works great. The other roll just has one led that is lit blue somewhere in the middle of the roll and is always on when power is applied, whether the data line is hooked up or not and whether the sketch is running or not. The whole roll flashes at first when power is applied (like normal) but then just the one led remains lit. Nothing else happens. It's hooked up properly (using the arrows on the led strip) and I'm just swapping the data/gnd lines (blue/black pair) from the roll that works to the one that doesn't. Rebooted Teensy, etc. I'm using a 5v60a switching supply powering the teensy/octo as well as the strip and the gnd lines to each are tied (at the power supply).

I'm using an Octo2811 just as a level shifter with a Teensy 3.2 and only have one line hooked up (using orange pair on TOP ethernet port) and just using "DATA_PIN 2" in my sketch for the data line input. I'm not including the octo library at all and only using pure fastled, if that matters. It's just running the DemoReel100 demo.

I really don't know where to start troubleshooting this. The thing that is confusing is why it's just a single led in the middle of the strand that's lit.

I measure 5.1v going in and 4.875v coming out the other end of the 4m strip, which seems about normal with nothing except one led lit.

LEDs on strips not working is pretty normal just one the scale of things in manufacturing terms. Hence why you can now get a WS2812 varient with a spare input designed to automatically daisy chain dead pixels for use in big LED walls where things work for a couple of weeks and then blow in the middle.

What is a bit unusual is it not getting caught in QC from what I thought was a mid to upper tier seller. Would be expected from bottom end of Ebay but may be an actual defect from shipping here rather than unloading dumpster dives on people.

Suspect the controller in the LED is dead and you either need to cut it out of the strip or start talking refund with the seller. Posting pictures of the working and non working strips will help there, and assuming you don't exceed the current capacity of the PSU you should be able to actually have both strips running off the same output and therefore showing the same pattern (modulo your dead pixel).