I had this happen a second time to me... now I know it wasn't due to a Verizon signal outage... it's the Bionic. I showed it to the Verizon store manager where I bought it... they had plenty of 4G signal in the store.
He couldn't figure out why, and replaced it for me. If it has something to do with not being able to reacquire a signal after being disconnected, then I know where it happens... at work in my office, hardly any signal at all most times. So when I get to work, I'll switch it to airplane mode and then take if off airplane mode when leaving the building.
If it does happen again, I'll be back to the Verizon store raising holy hell about this $300 POS that can't get it up on the LTE network.