I can't say for sure the carrier update caused the problem but the timing fits.
My phone has worse reception after the carrier update a few weeks ago. Can I "downgrade" to the old one? Seriously, I have fewer bars in the same areas as before and I now often have people say they have a hard time hearing me like there is a bad a connection. This never happened before the carrier update and now it happens fairly frequently.
I should also mention that I have tried several types of resets including network reset and clean wipe and reinstall ofthe phone. still have the 18.1 carrier settings though. still often have a bad connection where it used to be good.
Then I could not tell you anything else according to forum rules. And, if that's the case, and you didn't already know, then you should probably not try.