I'm in an organization where we are deploying eight (8) MiFi 4620L's and experiencing the exact same symptoms. One of those eight did update to 3.20.03.01 successfully, the other seven have not.
I called Verizon tech support. They had me go through the reset process, etc..and after no success, they gave me Novatel tech supports phone number (877-259-2761) where I had to deal with someone even less knowledgable in India who had me do the exact same troubleshooting steps that I had done and that Verizon support had me do.
No luck and I'm waiting for a call back from Novatel after the tech discusses with his supervisor what to do next.
Everything looks great, until the device shuts down to update and it appears to just restart saying the update was successful. I didn't do anything different on the one MiFi that did update successfully.
I'll keep an eye on this thread if anyone posts more info. I can't believe we're the only ones experiencing it, but a Google search yields just this thread so far.