Apple is currently looking into the iPhone XS LTE issue, which affects some owners of the iPhone XS and XS Max.
[iPhone XS Tests Far Better Than iPhone X in LTE Speeds]
iPhone XS LTE Issue
According to an iPhone XS Max owner Apple is carrying out a research program with some customers experiencing LTE connectivity problems.
Apple asked him to install a baseband logger to track his cellular connection. Other owners have confirmed being asked to share device logs with Apple engineers.
Symptoms of the connectivity problem includes fewer bars and poorer signals in these iPhone models. However, it sounds like it only affects a certain number of users, so it’s not a universal issue.