A few OnePlus 3T users have been facing an issues with VoLTE after updating to Android 7.1.1 based OxygenOS. The update in question is software version O2OS 170324 which was released last month.
As seen in the screenshot above, the button to enable VoLTE has disappeared from the Settings app for certain users. For some, the feature is still working, and they are able to make calls using VoLTE. But for a few unlucky users, the feature doesn’t work.
It’s been more than two weeks since the issue has appeared, but OnePlus hasn’t even acknowledged the problem. Even Indian users with the Jio SIM are facing the issue after the update to version 4.1.3. The bug appears to be present in the latest Open beta as well.
Hopefully, OnePlus fixes the issue in the next OTA update. Have you been facing this issue after updating your OnePlus 3T to Android 7.1.1 Nougat?
via OnePlus Forums