Have you tried the 871 beta? (https://hakenaudio.exavault.com/share/view/1dt2a-7t6ul9ue)
I’m on Mac Mojave and both the beta and the stable release loaded fine here. Although with the stable release, on loading, I got the warning that the software was 16 bit and not likely to work for much longer on my system. Maybe related to your issues? I got no such warning with the beta so I imagine that is 64 bit.
Like I said, the only way I could get the Editor to work nicely was to give the Mini a USB port of its own on my Mac. Once I did that its all been fine. The iPad editor app also works fine here which is useful for tweaking but you can’t access the full depth of the Matrix using it. The powered Apple camera connection kit provides enough juice for the Mini and the iPad together.
i just used a TRS adaptor to connect an expression pedal. The constant 3v DC out will probably be for the pedal. I think that input senses the connection and sets itself up to behave in the right way. If you want to use it for CV out you need the CVC hardware but I think its an either/or thing on the Mini. You can have a pedal or you can have CVC. Don’t think you can have both.