@Forms - dhave you upgraded to the latest firmware?
you can see Squarp explicitly listed the Akai MPK mini MK2, so Id assume they believe it is working.
a general point of note here… (not to Forms specifically … )
Im a software developer (not connected with Squarp) and done some USB midi work with micro-controllers…
USB Midi has its ‘vagaries’ , just because one device does not work - does not indicated a ‘general fault’ with usb midi, rather just an incompatibility between devices. (so the QuNexus was having issues, does not really say much (if anything) about an Akai not working ;))
one thing, to always check with USB is power - its probably the most common fault Ive seen.
if a USB controller has the option to use external power (as well as bus power) , if you have issues, try it with external power rather than bus power.