I have a Jetpack 4620 I have had for some time. I would use the menu option to retrieve the current data usage for my dataplan. This feature no longer works and I don't know what caused it. Sometimes it would display a "Data usage is not available at this time" message. I would wait a little bit, then try again and a message would eventually be displayed showing my current GBytes used. Now it always shows that Data Usage is not available message every time. Fortunately, there are other ways to obtain this information, but not being able to do this when using the Hotspot is inconvenient. I will be making a trip to the Verizon store for more investigation and I'm sure they will make me buy a NEW Hotspot. Otherwise this hotspot works fine.
Do the usage stuff… turn off the Jetpack, remove the battery and the SIM card, wait a minute and reassemble the Jetpack leaving the back cover off. Power on the Jetpack and let it sit for a minute or so until it reconnects to Verizon. Next, press the Master Reset Button as described on pages 5 and 82 of the user guide. Note the Jetpack does as described on page 82 after pressing and holding the reset button until the LED blinks green. Once you do this you will lose any custom settings in the Jetpack so be sure to note things like SSID and Wi-Fi password before you reset the device. Allow the device to restart and connect to Verizon. Log into the device as described on pages 21-33 and make any custom setting changes as necessary.
MIFI 4620L User Guide:
The usual stuff didn't work... the factory reset button did not work either. Went to the Verizon Wireless store, told them my problems with the Jetpack and they gave me a newer Jetpack model with everything working for free. Well, not really, I ended up upgrading 2 smart phones and they took care of this, too. So the problem was sorta solved by turning in the old unit. Actually, they let me take it back with me and I'll dispose of it as e-waste.