The issue was outlined on the MacRumors forums, with complaints first popping up back in April 2018. MacRumors reader marmiteturkey explains the problem:
I have an approx 1in spot on my iPad Pro screen which is brighter than the rest of the screen - it's unevenly lit. The spot is about 2in above the home button, and although it has soft edges, I'm anal about my gadgets, and the difference in brightness could be described as 'minor', it's clearly there. It looks a bit like a pressure spot or similar. I always keep it in a case with a screen protector and the Smart Keyboard, so it's well looked-after.According to iPad Pro users who have the problem, it appears to be an issue with uneven backlighting in that area. MacRumors can confirm the problem, as we have a 10.5-inch iPad Pro on hand that appears to be experiencing the same issue outlined on the forums.
Customers have been complaining of the problem for months now, though it continues to be unclear how many iPad Pro models may be impacted by the issue. It is not known if a similar issue will impact the new 11 and 12.9-inch 2018 iPad Pro models, as these devices are too new and the problem appears to surface after several months of usage.
Multiple users who were affected with the bright spot on their screens have been able to take their iPad Pro models to Apple for a replacement, but users who are no longer under Apple's one-year warranty or AppleCare+ have not had luck getting a free replacement device.
Out of warranty, Apple is asking customers to pay the display replacement fee, priced at $449 for the 10.5-inch iPad Pro and $599 for the 12.9-inch iPad Pro.