If the issue occurred after the display was removed, something must have happened in the course of the repair. If it is only one stripe of the display, it's possible that one of the pins on the connector is not making a good connection, perhaps because it is bent, not seated properly, or there is something in the connector preventing it from making a solid connection.
It could also be that there is some minor damage to the cable responsible for touch function, or the digitizer itself.
Whatever the reason, it is certainly worth opening the iPad up again and having a look. The digitizer connector is the middle connector of the three that come off the display, the long one. Make sure the accompanying cable is free of damage.
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