I use an MC6 Pro (was using an MC6) with the hub, C4 and Bass UW as well as many other midi controlled pedals.
I have had my share of midi issues.
My latest ended up being a bad TRS cable for an aux switch that I use to bank up and down and page switch on the MC6 P.
That bad cable played all kinds of havoc on my midi set up.
Things I have found useful when using the S/A hub. Put the hub last in the midi chain , This had the greatest impact on many of my issues. I'm not sure why it matters, I just know that it solved some issues I had a long time ago. I have since moved to a midi splitter as opposed to daisy chaining my midi cables.
I haven't read the whole post so some of this may have been covered.
Do you have midi cables running out of the MC6 and back into itself? If so, make sure Midi thru is off.
Also, for reasons unknown to me the order / construction of my midi messages on the MC6 mattered. What order I put things in while building presets.
It could be an unknown bug in the Morningstar firmware. Is it a new final firmware or a Beta.
Maybe check out the Morningstar forum. James is very helpful and very quick to respond.
Midi can be finicky and drive you crazy but when you get it working to your needs it's great.
Matt
Hey Thanks! v helpful, will check