I upgraded without problems but…
I am using MC6 with its USB connected to an IConnectivity Host Device, and it has always been working ok with previous firmwares.
But here, the IConnectivity USB Host no more recognizes it.
This could happen when a device is not USB compliant.
If it could help solve the problem, with my Elektron models:Cycles and Samples, when I program their USB to manage MIDI and AUDIO, I can’t pilot them with my IConnectivity MIOXM or IConnect Midi 4+, but if I remove the audio part from their USB (a setting feature) everything is Ok.
As you have changed something on the device USB Id, it could be related.
I hope you will solve this issue because I had to revert to 3.6.2 without the very interesting features of 3.7.x.