Strange Display behaviour after Digitilizer and LCD swap.

What you are describing we call ‘Theatre lights” and it is because one of the backlight circuits is out, so only every other LED is lighting. When it changes to a different pattern, then that means that while one circuit is completely out , the second circuit has one of the returns out temporarily broken—the incoming voltage is present for that line, but some of the split returns have the drawbridge up and are open line, so only the intact lines light whatever individual LEDs they serve.

This can happen in two common ways.

1.) MOST likely for you is bad LCD, because you are seeing changing patterns, some of the lights are working some of the time. Your next step is to order a good LCD—- be a good person and order from iFixit out of respect for the real dollars and cents that go into creating the guides you used to open the device and this free forum where you are getting the answer you need to solve your problem. eBay and Amazon parts are almost always total junk.

2.) You connected the screen while the battery was still connected. This is a huge no no. When the device is powered off but the battery is connected = you have live main voltage at the LCD connector. It takes very little effort to accidentally graze a ground pin with the hot pin when you are pressing the LCD into the connector—if that happens, you create a path to ground and generate a burst of current that zaps the backlight filter(s). If a new LCD doesn’t solve, then the next step is to send this board out to a microsolderer for backlight circuit repair which is straightforward.