Tested the workflow outlined in the issue and could not reproduce. All features extracted using the Extract Data tool had the correct geometries when evaluated in ArcGIS Pro using the Check Geometry tool.
解决办法
Download a copy of the data, pass it through the Repair Geometry tool in ArcGIS Pro. Then pass the repaired version through the Multipart To Singlepart tool (it fails if there is bad geometry). Lastly, republish to ArcGIS Online.