Controlling more than 8 channels using the MIDI Remote

Why is it for me such a hassle to do the following:
Cubase 12 pro, 2x Behringer Xtouch controllers, to control 16 or more channels?
I checked WinRt. Not possible though to assign 2 the same model controllers. The second controller even coded with different midi settings.
I just want to make a mixing console with 24 faders instead of 8.
In the midi remote I choose APC MINI for chan 1-8. Works fine
For channel 9-24 I use MIDI Mix. In the Mini Remote I choose (options) 16 channels and make the connection with the Midi Mix. Works fine. I save the file.
Now I open the file again, and the software forgets channel 9-16. Instead it’s back to 1-8 (MidiMix).

The client service is in adequate to answer my questions (2 months and still no answer).