LG G5 not staying connected to 4g-lte
I have a new LG G5, under android 7 am having an unusual connectivity issue. I will be connected to 4g-lte, sitting in a place with fine 4g-lte service, and at some point, the connection drops down to "H" and pretty much stays there indefinitely, until I do one of the following:
1) Restart the phone, or
2) Go into and back out of airplane mode, or
3) Go into settings>Networks>More>Mobile Networks>System Select>Network operators> (and there either "select automatically" or search networks and specify the at&t lte rat).
That pretty much always puts me back on 4g-lte for a while, sometimes 15 minutes, sometimes a few hours, I can't detect any pattern.
I've taken it in once to an AT&T store, and we replaced to a new sim card, and they played with some Access Point settings, but didn't make a difference.
The phone is new to me, and I upgraded to Android 7 first thing, so I don't know if it was happening under Android 6. I have seen one user with the same phone who says it happened only after upgrading to Android 7.
Note also that this is a non-AT&T version of the LG G5, but is one with compatible bands, that is not the issue. (This is the RS988 version, the LG factory unlocked version, not the H820 AT&T version.)
I'm hoping to not need to go down the whole factory reset path, but am running out of options to try! Any thoughts?