Looks like the NI 9220 is not supported by cRIO scan mode:
http://www.ni.com/white-paper/8136/en/
It's mostly a sign of inadequate communication between the hardware and software sides of my project, but this threw a major wrench in my gears recently. I wasn't anticipating any difficulties like this because it doesn't seem like a super exotic module. Anyone know if there are plans in work to have this module supported?