Hi Brandon,
I discovered (with the help of an Esri Analyst) that the Append function to a hosted feature layer in AGOL cannot handle related tables. My survey had repeats, so I was out of luck going that route. We tried using the Append geoprocessing tool in ArcGIS Pro, and was able to update the parent table successfully. However, the Global ID was not preserved and the related tables were not updated.
The Analyst logged these enhancement requests:
ENH-000113718 : Allow Workflow or ability for Survey123 to load, or append all records from a previous survey that included Repeats, i.e relationships in the Hosted Feature Layer.
ENH-000113717 : Add ability or workflow that would allow Append operations to preserve Global ID for hosted feature layers with relationships .
He suggested these workarounds:
-For Survey data without repeats/relates: Append In Pro to Hosted Feature Layer
-For Survey data with repeats/relates: Append in Pro using Preserve Global ID to Enterprise Geodatabase.
Thanks,
Shana