I have 2 of these phones in my family and noticed the problem occurs especially whenever the charger is inserted. Solution I think is to replace the USB charging connector. I am currently searching online for a replacement part and will update if I found it and do the replacement.
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=== Update (05/31/2019) ===
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I have tow of this phone in my family and noticed the problem is amplified when the phone is being charged and handled. I think there is a defective charging port that needs replacement. I am now searching online foe a replacement part. If anyone fine a supplier, please post website address. I will followup if I am successful.
I have 2 of these phones in my family and noticed the problem occurs especially whenever the charger is inserted. Solution I think is to replace the USB charging connector. I am currently searching online for a replacement part and will update if I found it and do the replacement.