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My phone contacts started displaying incorrectly, randomly switched or mixed up with other contacts. Why is this? How can I fix this?  I have a Samsung Galaxy Note 4, with recent update to Marshmallow 6.0.1.  This updated has caused several issues, including this issue, major battery drainage issues, wi-fi  connections issues, instability.  Please help in addressing these issues. I have searched extensively through forums and online, and have been unable to find any fixes.