Who I have the same questioned this topic

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? 

Thanks!