I know there have been issues with the latest update in different ways. I also read folks in the S9 have this issue. Mine is the S9 plus and it is also stuck in 3g. This began immediately after I downloaded the update. None of the tricks online did anything including a factory reset so I'm thinking that's a misnomer. It didn't reset it to factory. Anyone get any satisfaction from Samsung yet? It is obviously their fault.
I got mine to stay on LTE by downloading an app called ForceLTE this gives you the radio statistics menu that you should get when you key in *#*#4636#*#* but Boost Mobile has that function disabled. The phone stays in LTE when you select "LTE only" then cycle airplane mode off/on. This is only a workaround though because you will still have to switch back to "automatic" to make or receive calls. This bug is effecting the S8 as well, there were 2 that came into the Boost store with the same issue when I was there.
Im having the same issue, however neither boost nor samsung admitted the issue. both claimed the network in my are are good and that its the others co issue, boost vs samsung. two days 3:46 minutes of boh boost tevh and samsung tech issue continues.
I have the same issue have done eveything and still no luck - stuck on 3G with Boost Mobile - no help from Samsung/Boost
I think I will buy a different brand phone and go with another provider. If they don't care to help then why give them our money?