I'm currently using the Nucleo 64 board with the STM32F446RE chip.
This microcontroller has 3 ADCs, which according to the reference manual (see pic), can be configured to run as ADC1+ADC in simultaneous mode, and ADC3 independently. This would be for my configuration, MULTI = 0b00110.
In this way I can use the ADC1+ADC2 to simultaneously sample current, and do other stuff with ADC3.
However, in CubeMX when I select Mode as "Dual Regular Simultaneous Only", ADC3 gets locked up in that same configuration (see pic).
Unless I misunderstood the Reference Manual, something would seem to be wrong.