While normally I would say that those three spots, or “smudges”, on the bottom of the screen appear to look exactly like some I have seen before caused by wear and/or excessive pressure against a specific spot, it looks like multiple others have reported spots in approximately that area on the Surface Pro 5th, 6th, and 7th gen: [post|373243][br]
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This makes leads me to potentially the same conclusion as they came to - that it may be a known, but not owned by Microsoft, issue caused by design which puts too much pressure over time on that area of the LCD, causing those pressure points/damage to show. [br]
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I would appreciate a second opinion from another though.[br]
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Best of luck.