I got it 5 months ago in my s8, two main reasons don't use your phone in high brightness for long hours & don't use white backgrounds, if possible use XDA gesture navigation bar, it hides your current navigation bar. I got screen burn of navigation keys so replaced it with xda gesture navigation bar. https://play.google.com/store/apps/details?id=com.xda.nobar
We apologize for the inconvenience caused. Regarding your concern we would suggest you to visit nearby Samsung Service Centre in order to get your device physically inspected by the Service Engineer. Please find service centre details in the link provided -http://www.samsung.com/in/support/servicelocation
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