hey dan…
Looking at this now and I think the dmesg output might be a red herring.
It’s likely to do with the M4 showing up as both a ACM device and as a MIDI device.
Do you see this error in Maiden - about 6-10 seconds after connect the M4:
>> ttyACM found, but not a crow
dev_list_add: error allocating device data
?
EDIT - testing now on shield with molly the polly and I’m not seeing a UI freeze (although - I was just on an older version of molly… updated and still not seeing UI freeze, but did get a random stuck note or two.)