Nice, so i guess this confirms the parsing issue specifically happens when an address family (like ipv6 unicast) is added to the command here. I guess to get deeper into this, you could update the code to print more, some more debugging outputs, or/a...

https://www.wwt.com/atc/atc/overview

World Wide Technology's Advanced Technology Center (ATC) has quite a few ACI labs on-demand, for free. FYI - You cannot register with a public email domain like gmail or yahoo. WWT doesn't charge for the labs--on-demand or scheduled.

Are you referring to this: https://www.youtube.com/watch?v=gk2TanYjX7I