My phone, which has worked great for over a year, recently (maybe after the Oreo update?) has lost 4G LTE capabilities. When I am connected to wifi, my mobile network is connected at 1X. When not connected to wifi, the most I ever see is 3G. This is happening all over (so it's not a location issue), in places I have always had strong 4G in the past, and in places where other people's phones are still seeing strong 4G signals.
When I restart my phone, 4G comes on for about 10 seconds, then drops out and reverts to 3G.
I have tried switching mobile networks, resetting network settings, and rebooting the phone.
Any thoughts on how to fix this?