Screen

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

If this test suggests that you do have a hardware fault, you would be beet advised to seek assistance from an Apple Store or Apple Authorised Service Provider (AASP) where your iPad can be properly tested - and if repair is required, you can explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

Alternatively you can use Apple’s mail-in repair service:

iPad Repair - Official Apple Support

It looks like a hardware (screen? other internal component?) failure but we, just users like you, cannot diagnose that issue remotely, sorry.

I suggest that you contact Apple Support directly (they have tools to run remote diagnostics), using this link:--> Get Support or make an appointment (*) and have your device inspected at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> Apple – Location Selector. After checking it out, they'll give you all the available options.

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.