Back in mid-September, I was out shopping and experienced this issue for the first time where the Thunderbolt wouldn't keep a 3g connection. It could still lock onto 4g, but I intentionally keep 4g disabled for battery-saving purposes. Mind you, the Thunderbolt was stock and was running on Froyo 2.2 at the time.
I spent about 30 minutes with Phone Tech Support and the L1 tech said there were no outages or service issues, and didn't know how to address my situation. At that point, I had demanded to speak to a manager and he said the only thing he could do was open a service ticket, and that was it. Both the L1 tech and the manager blamed it on some silly coincidence/maintenance work excuse that made no sense.
That same afternoon, I went to a brick & mortar Verizon store and the Manager there blamed it on the fact that I used apps like LTE On/Off and JuiceDefender. His explanation did make sense at the time until I got home and did some research that debunked his excuse.
The solution at the time was to hit ##778# > Password: 000000 > Modem Settings > Rev. A > "Enabled" (instead of eHRPD). That fixed it until...
Earlier this week (mid-December), I started experiencing this issue AGAIN. This time around, the Thunderbolt was still Stock but it's running Gingerbread 2.3.
- While I was out shopping, I switched to 4g mode to quickly research on why this was happening. Stumbling upon the ##778# solution, I tried it again EXCEPT the Rev. A. setting was already set to "Enabled" (instead of eHRPD).
- I've toyed around with Turning the Radio Off and then On again, via the "LTE On/Off" app, which worked once. However, the phone wouldn't lock back onto 3g.
- I've tried Enabling/Disabling Airplane Mode and that didn't do anything.
- I've confirmed that the Network Select has been and is still set to "Automatic" (instead of "Home Only").
- I also tried disable and enable the "Data Enabled" feature in the Settings menu. It worked THIS time, but I would not be shocked if this problem will continue to surface again in the coming days.
Here are a few other facts that I've gathered when reading around other forums:
- Apparently, rooted users are experiencing the same issues.
- It would not shock me if the Thunderbolt's Gingerbread delays were related to this issue, and how it has been difficult to diagnose, replicate, and correct.
- Also, I've stumbled on other threads indicating that non-Thunderbolt 4g users are having the same issues. It leads me to believe that this might be a Verizon issue related to the Handshakes/Permissions for phones that are equipped with a 4g LTE radio.