First of all, kudos for properly testing the screen before sealing it up. It’s a critically important step that many folks ignore.
It’s not uncommon to have bad digitizers, especially if you bought one off of eBay. The first thing to do is to verify that the digi is properly connected and that the connector isn’t damaged in any way. Those ZIF connectors with the flap have to close uniformly otherwise some of the connections from the flex will not make proper contact and therefore you will see a “dead zone”.
If that looks good, then you probably have a bad digitizer. Have your vendor replace it or order one from a reputable vendor like iFixit.