Is the line there in the same place for every model and effect? or is it just the Sweep Echo model that is displayed incorrectly?
I don't believe that a factory reset would address this sort of issue if it was software related, you would need to reinstall the latest flash memory to address any sort of software issue like that. We have instructions to do so available at the link below:
Definitely try a re-flash of the firmware.
However, from the looks of your photo (thank you, by the way), that single vertical line of missing "pixels" looks more like a bad LCD display screen. You should get your unit to the nearest Line 6 Authorized Service Center tech for them to verify and replace the screen: http://line6.com/support/serviceCenters/