Append tool slow for ArcOnline Users but fast for Administrators

[LindsayRaabe_FPCWA]

We rely on the Append tool to update a number of feature services on a semi-regular basis. We have recently discovered that when appending data to a feature service, the tool works super quick (seconds) to append thousands of records when run by and ArcGIS Online administrator. But for Non-Admin users running the same tool, with the same input & target data, using the same PC & network connection (essentially everything is the same except their ArcGIS Online member role) it is super slow (hours). 

Why????

I even tried a custom role where I toggled the below setting, thinking that looked like the most logical setting that might make a difference, but alas - it had no effect. 

[jzcgis]

Any updates? When I use the append tool to append features to an item in enterprise, it is painfully slow. 80k features takes almost an hour. I tried doing the same in Pro and it was actually slower.

[Robert_LeClair]

I'm showing BUG-000154190 is currently "In Review" as it's current status.