I've nailed it down to one of my Combobox fields. When I remove the field there is no error. When I add it back then the Patch error:
"Error reading string. Unexpected token: StartObject. Path 'Value', line 2, position 13.\r\nclientRequestId: 9c607a94-2e32-4511-9685-b89dad844de0\r\nserviceRequestId: a21430a1-1037-0000-2dcd-bce661b6caf0"
Here are the property settings:
Items: If(varShowLaborFields= true,Choices([@'My SharePointList'].'Cost Element'),Distinct(Filter(
'My SharePointList',Vendor=cmbVendor_1.Selected.Value),'Cost Element'))
DefaultSelectedItems: ThisItem.'Cost Element'
Update: cmbCostElementOpp.Selected
NOTE: I have nearly this same field configuration in use on another form in my app and it works fine. I've removed the field, added it back again. still same error.