Still waiting on an answer. Several helpful community members and Verizon staff have commented with a few questions about the situation, but no steps for troubleshooting or resolution were mentioned.
I purchased a Verizon-branded Google Pixel 3 XL in-store in November. I started experiencing an issue right out of the box. If my Pixel 3 XL switches to 3G because of any reason, it will never switch back to 4G LTE on its own. I can toggle Airplane Mode on and off, even reboot the phone. It will not switch back to 4G LTE even if I am standing mere hundreds of feet away from a Verizon cell tower.
The only workaround I've managed is to go into "Settings - Network & internet - Mobile Network - Advanced - Preferred Network Type" and change that setting off "Global" to "LTE / GSM / UMTS" and then back to "Global". It will then happily work on LTE until the next time the signal degrades to the point where it switches to 3G where it will again be stuck until I perform the steps above.
I have waited on new OTA patches, I've documented signal strengths detailing my phone's refusal to switch back to LTE even when RSSI is in the -70s (Airplane Mode and reboots to no avail). I find it very discouraging to find my thread where I documented this removed with no resolution or given reason.
I'll ask again, can anyone please suggest something that can be done to troubleshoot this issue? I would be happy to investigate further.
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I'm having basically the same issue except none of the fixes mentioned have worked. Went to bed and woke up and now this is apparently an issue. Shows up as roaming all of a sudden despite no changes being made in my location.
Being able to get the signal you need is crucial. I wouldn't want to get stuck on 3G either. I'm glad to help. How often is this happening? When it happens, does the phone ever go back to LTE on its own? What are the zip code and nearest cross streets to where this is happening?
This is happening to me as well, on a factory unlocked pixel 3 xl straight from Google. I recently switched to VZW prepaid and in the last two weeks of service have gotten stuck in 3G as described by the OP. I did also have an issue with my phone saying it was Roaming, connected to "Preferred Network", however I resolved it by the steps in this thread: https://support.google.com/pixelphone/thread/15864710?msgid=17108173
I will say, thank you because the only way I got this issue resolved last time it happened was to factory reset. Your method of switching network type to GSM and then back did resolve the issue, though I had to leave it on GSM long enough for it to connect properly as LTE then swtich back.
I'm in zip codes 44319 and 44312 regularly (home and work) and it is happening in both.