I lost the Voltage tab in System Tuner or 3C Toolbox!?

The voltage tab has not been removed and will never be.

This can be due to one of the following:

1. The kernel was updated and it does not support voltage control
2. The kernel was updated and System Tuner or 3C Toolbox do not support its voltage control interface
3. The app lost root access during the update due to SuperSU requiring confirmation on app update (this can be disabled in SuperSU settings).

If unsure, please send a support request from the app settings with a note on the issue your experiencing. From the report I'll be able to figure out which one of the above is the issue.