That looks like a hardware issue for sure. I'd contact the seller or manufacturer.
First thing that comes to mind is an anomaly in the sensor, given how sharply it cuts off. Sensors like these may consist of a number of separate sensors glued together and it's conceivable one of them happens to not be performing on-spec in this array. That's just thinking out loud though.
In terms of trying things that may or may not help - carefully clean the entire platen, especially the edges. On transparency scanners (I'm aware you're scanning prints here), the first strip of the glass is often used by the scanner as a calibration area. If there's any dust etc. there, it'll produce a longitudinal band. There's a very slight chance something like this is happening in your device. But it's a long shot, really. I think it's more likely this is something that'll require a hardware fix/ replacement.