@dandan_1976 - I have exactly the same issue with player freezing and resetting when locked. I have discovered that this happens if the following conditions are met:
- music files are played regardless of format (does not happen when playing FM radio)
- backlight time is set to 5 or 10 seconds.
I am currently bypassing the problem by setting backlight to 15 seconds. Check if it works for you.
Sandisk support offered me to exchange the player but as the procedure takes a few weeks I learned to live with it.
