Stable 8.1.9.0 - Cannot Select 2g Network For Sim 2

[stefano nardi]

Hi!
Brand new Mi5, unlocked bootloader, stable 8.1.9.0, SIM1 is the one used for data. Sorry in advance for menu items, I'm translating from Italian.
In SIM settings - SIM 1 menu I can choose the preferred network type (4G/3G/2G), but this option is not present in SIM 2 menu! If I manually choose a 2G operator (in my case Vodafone) for SIM2, next time I reboot it connects to Vodafone 3G. Furthermore, if I select 2G as preferred network type for SIM1, SIM2 still connects on 3G.

Is there a way to keep Sim2 "locked" on a 2G operator, in order to drain less battery?

Thanks in advance!