We have finally (hopefully) sourced the problem we are having with editing a line feature class in ArcGIS Online. We are working on setting up a proxy page to fix/test this. We are using service in ArcGIS Server (not hosted in AGOL) reading one of our SDE databases. However my whole point of this project is to use it in ArcGIS collector because the technician has to use a smartphone). So even if we get the proxy page to work with the application template, that will not affect the ability to edit in Collector (or I assume ArcGIS app) since that reads the web map and not web app. The documentation is pretty sparse and I am not getting much response from the ESRI support analyst so I though I'd post this in the meantime.