I had the same issue and thought it could possibly be a faulty screen connector, so I decided to remove the LCD assembly. I didn’t have a good enough heater for the screen adhesive, so when halfway through I decided there was too much resistance prying it off, I put the phone back together and now the issue is no longer there. I haven’t tried any other fixes prior to that (kinda reckless, I know, going for the intrusion option straight away, but I wanted to play with my new ifixit pro toolkit, so cut me some slack haha), and I think it may have been a screen bend issue.[br]
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Hope it helps.