You may have already completed this diagnostic, but completeness of reply, I’ll outline it anyway…
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
With the suspected defect evident, perform a forced-restart of the iPad:
- On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.
- On other iPad models: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.
Should the display fault remains after restart, you almost certainly have a hardware defect that cannot be resolved short of having the iPad repaired. Ideally you will need to visit an Apple Store or Apple Authorised Service Provider (AASP) where your iPad can be assessed - and your options explored. Don’t forget, an AASP may be closer than your nearest Apple Store:
Genius Bar Reservation and Apple Support Options - Apple
Your alternatives are limited. Apple do offer a mail-in repair service. You have a device warranty, so repair cost should not be a consideration or concern:
iPad Repair - Official Apple Support
Your remaining options are to (a) live with the issue - or (b) simply replace the iPad with a new device.