Thanks for this post. I have been noticing that my clock also is off by 4 hours sometimes inside my building. I didn't think to check that it was carrier related but will check it the next time. I do roam onto other carriers inside the building unless standing next to the front window.
I hope nobody is afraid to bring anything to my attention..? I know there are Samsung changes that I need to get in there. Just the same old song from me, haven't been able to get enough time to update the app. It does weigh on me, I take a lot of pride in the app and hate when updates lag! Unfortunately real life (and real job) have to take priority.. stop if you've heard this before.. 😉
I agree, build your own. Sierra Wireless modem with a USB enclosure for it will let you use any router that supports Openwrt basically. I'm using one with a Netgear R7800 and it works very well.
The Sierra Wireless MC7455 has a bug that causes it to disconnect 1-2 times a day that may be fixed in the newest driver (I'll know for sure within a couple days), but is the only one that supports B25. They have other modems that don't have this issue, but lack B25. If you don't need B25, get a model that does 3xCA B41.
Check out the ROOTer firmware (build of openwrt with mods for LTE modems) https://www.ofmodemsandmen.com the developer is almost done with a new build using the latest openwrt, and you can get the pre-release builds on their forum thread (might be required for some routers). He seems willing to add any routers not listed as long as they work with openwrt.