I have a Galaxy S8 plus and I use AT&T. I never had poor phone reception till I got this phone. I was having calls dropped and bad clarity. I exchanged it for a new phone and got a new SIM card, reset my network settings and nothing fixed it. Then I found out that if you turn off the "ENHANCED LTE settings" it can fix the phone reception. So far it's fixed it. Let me know if you had a similar problem.
Just be aware that I had this turned off on My Galaxy S7 for similar reasons, but whenever my brother on an iPhone sent me a long text message (not sure how many characters, but a lot), I would never receive it. Never had this issue with anyone else, but he was dealing with my parent's estate after they both passed away suddenly, so it wasn't typical to get as long a message from others. But once my wife sent me a long one that I missed and I realized there must be something else going on (not just my brother's iPhone).
After I enabled this option again, I never had a problem again. So if you have this disabled and realize you are missing texts, either have your them send you shorter texts or re-enable this option.