Thanks for the report! I am unable to reproduce this. Using Logic 10.6.1 on macOS Big Sur 11.2.3, I can load any of the Analog Rytm Multi-Out configurations. Are you using a specific Logic project when the AU plugin only loads the stereo configuration? Does the same thing happen in a new Logic project?
The Analog Rytm standalone plugin also does not crash when launched when I attempt. Try closing all other applications and make sure nothing but the Analog Rytm MKII is connected to the computer and let me know if the standalone plugin still crashes then. Connect the USB cable to your Analog Rytm MKII before powering it on. Please also attach a crash report: How to extract logs