ok, thanks to huge help and patience from @GoneCaving , we tracked down the issue.
and there is now a fix for EigenLite (dev branch) and EigenD (2.2 branch)
for those interested…
the issue is when we connect to usb devices we tell it to use a configuration.
it appears on some Mac/macOS combinations this takes a very short time to take effect., on others it is instantaneous - so for some, this results in the ‘interface’ not being ready in time.
my suspicion is macOS, at some point in time, changed this behaviour/timing ever so slightly.
to fix, Ive introduced a very short delay (1 millisecond) to allow the pico to update its configuration before querying interface, and this seems to fix initial connection issue, and also re-connects.