Well,
I have had my 2015, 12.9 inch iPad Pro for a little over 4 years, now and I have not had this issue.
It's the backlight panel seperating/delaminating from the LCD screen that is causing this issue.
This is not a common occurrence, I am afraid, and does not affect every iPad Pro model.
Hopefully, it will not get any worse.
If it does, you should be aware that iOS devices with the Home button fingerprint ID sensor, the Home button and sensor may not function properly after the screen assembly is removed and replaced.
Only Apple has the appropriate hardware and software reset codes to be able to reset the Home button and ID sensor back to working order in a repair situation.
Most repair shops that claim to do and have experience/expertise repairing Apple mobile devices DO NOT have access to these hardware/software reset codes ( and in some cases, no access to genuine Apple parts and/or maybr good parts cannabalised from dead, non-working Apple devices and computers ) and this will render the Home button/finger ID sensor pretty much useless.
I believe Apple did this on purpose to discourage third party repair and repair shops from ever being able to fully repair any Apple mobile device.
Apple is very anti third party repair and these suuport communitites discourage us here from ever recommending any known reliable and expert, so-called, “unauthorised” Apple product repair facilities for users to either travel to or mail their devices or computers ( laptops ) to.
You maybe better of just paying for and taking the replacement iPad from Apple, in the future.
Best of Luck to You!