The top cable is for the earpiece speaker and proximity sensor. Middle connection is for the screen including touch. The bottom connector is for the home button. I would disconnect the battery and check the connections with a magnifying glass and see if you have any damaged pins. If they are fine I would clean the connectors with a qtip and alcohol and a soft brush, reconnect and check it.
You could have damaged them while installing them. It's possible and the best way to find what is wrong is to make sure that everything else works until you get to the last possibility. And I have put on multiple screens on iPhone 8 plus and it has nothing to do with Apple. It's something that happened during the screen change or a defective part.
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