Anyone seen this error before?

I'm using Process Recorder to record adding BOM elements for P3002 W3002A. The form request records fine but when I put it into an orchestration and run it, I get an infinite recursion stack overflow error that cannot track down.
it's a com.fasterxml.jackson.databind.JsonMappingException
but the JSON in the request is very simple:
{
"Item_Number0": "aaaaParent",
"Branch0": "123456",
"GridData_1": [
{
"Item_Number1": "aaaaChild",
"Quantity1": "1"
}
]
}
The...

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