I preordered my galaxy S10+ after having my Note 8 for 2 yrs.
Since upgrading to the S10+ I noticed places I used to have perfect service started becoming less bars.
in areas I had ok service I would now have bad service.
I bought a new phone and ended up getting worse LTE reception.
Mind you I live in NYC.
A very well known carrier issue. You are not the only person. More of a carrier problem than a Samsung problem. There are many threads on here discussing these challenges.
I might recommend shifting over to Verizon if you can. Your phone should be able to be used on the Verizon Network