Hey Ryan,

Seeing the exact same issue. I do believe it's worthy of a HI ticket. However, as a work-around I've found two options:

1. Either change your Subflow Input to a "string" value and pass in just the SysID of the Assignment Group you're looking to use. (Make sure the assignment at the task level is using SysID as well - the system will recognize and fill in the missing details)
2. Perform a lookup of the desired Assignment Group before hand and pass the record result into your "Reference" subflow input. This somehow passes the "entire" record, rather than the stringified version.

If you do open a HI ticket - share the results if you can. Hope this help!

Regards,

Trent