I don't think there's any hope for an update to fix this issue; it's a Verizon network issue, and they have no clue about how to fix it.
My Thunderbolt's been randomly dropping 4g off and on for months. I live in a strong 4g area. All Verizon can tell me to do is power cycle/toggle airplane mode/pull battery/pull sim/replace sim/factory reset/wait for a call from technical support (which NEVER comes!).
Today I spent the morning on 4g, but I've been on 3g for a couple of hours now. I realized long ago that it's hopeless to call CS about this, even though I still do, just to make them put a record of my loss of 4g service in my file.
Well, that's certainly depressing! At least I now know that I can usually fix the issue by turning Airplane mode on and off or, if that doesn't work, turn the phone off and then back on. Other than that I love my Bionic.