If it does change the 'Max GPU Voltage' only a few numbers, i guess the software may adapts itself in correlation of the CPU load.
For example, mine does it from 1207 (default) to 1213 Gpu Voltage. When i hit the default Tab it goes back to 1207 and at next reboot it shows 1213.
If not a few, there's a prob in your settings.
Asus Dual RX480 O4G - Core i5 3570K - P8Z77-V LE PLUS - (still on 2019)