I bought my iPad Pro 10.5 in January 2018 without AppleCare+ (not available in my country). I'm using it for my university degree as a digital notebook with the Apple Pencil. I use the the Smart Keyboard Cover from Apple. other from that, I take care of the device a lot because of its importance for my degree.
It began showing the bright spot after 3 months of normal use. I used the warranty after 11 months of use and had it replaced no questions ask by Apple.
4 months afterwards the newly device started showing the same bright spot So I went to the Apple Store and they refused to acknowledge the issue and only offered to replace it to a new unit for 470 euro (lmao).
There's obviously a design problem and Apple is refusing to acknowledge it at the moment. I wish threads like this will force them to begin some kind of a support program.
They dealt with it right the first time. I'd book it in again and you'll likely get someone else who might just sort it for you no questions asked. Worth a shot, surely?