A reliable method to confirm a screen or other hardware fault is to take a screenshot when the fault is evident - and then review the captured screenshot image...
When reviewed, if the lines are not present in the screenshot image, then you have demonstrated that you have a hardware fault that, sooner or later, may become sufficiently severe that repair or replacement of the iPad are the only options. If the lines are visible in the screenshot, the something other than hardware will be the cause.
Note: When reviewing the image, rotating the iPad screen orientation by 90°, from Portrait to Landscape, will ensure that the image does not coincide with screen defects if present.
Take a screenshot on your iPad – Apple Support
As described, a hardware fault is very likely - for which the only remedy is repair. The technicians at the Genius Bar of your local Apple Store will be able to test and assess your iPad - and will be able to discuss your options. Otherwise, you can mail-in the iPad for repair.
Genius Bar Reservation and Apple Support Options - Apple
iPad Repair - Official Apple Support