I was having the same problem and hopefully I may have found an answer. For me it was switching to a different SD card. Nearly every time I had to restart my phone I kept receiving an error telling me scan my SD card. After doing this more than a few times I finally decided to try a new SD card and voila no more screen lock ups. Now this is not yet conclusive for it has been less than 48 hours since the switch but in that time I have not had to restart my phone which I was doing nearly every morning.
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