I would look at the Dev Tools as this point to check the values of the flow.
Make sure the payload sent to your function has the proper value being sent.
Validate the response is as expected.
Dump the views (CTRL+ALT+V), expand System Views, and validate that actionResult has a value. It may show null here. Assuming you had debugging turned on (CTRL+ALT+8) check the console. You should see some events in there for your row-update showing the values of actionResult at the time.