Anytime a Jetpack behaves erratically, pull the battery, gently polish the battery contacts to clean them on both the battery and Jetpack. Remove and reinstall the SIM Card to reseat it. After you reinstall the battery, turn it back on, wait for it to come back up and use the reset button to reset the Jetpack back to factory defaults. When it comes back up, login to the user interface and reconfigure the Jetpack to your liking.
See page 64 in the user guide:
Jetpack Settings > Jetpack > Preferences > Device Preferences > Sleep | Shutdown = Never.
Turn the display off after so many seconds, because the image will burn in to the display.