Apple recently released two updates of IOS 12.1.2 and fixed the issue of enabling the previous version of eSIM, as well as internet bugs in iPhone XS, XS Max, and XR in Turkey.
However, after the new version was launched and updated, many users still reported that their iPhone could not receive 4G signals and could not access the Internet. As a result, basic functions such as iMessage and 4G calls could not be used normally.
Do NOT Update to iOS 12! Why I Regret It
Some of the users have also reported problems with Wi-Fi not being able to connect properly after update. The IOS 12.1 has also become a sub-version with more problems in IOS 12 series.
If you are unfortunate to encounter such problems, the solution provided by other users is switch to the previous IOS version. Or by turning off the Wi-Fi Call function (Settings → Mobile Service) or turning off 4G voice calls. Settings → Mobile Services → Action Data Options → Enable 4G → Change to “Data Only”), and then reboot to solve the problem.