I was publishing a feature service merrily (doing the overwrite) until yesterday morning when it just failed. Somehow it's just gone in AGOL. Subsequent efforts to republish or even publish with a new name have also failed. It seems to be on the ESRI side. The message is:
"Packaging succeeded, but publishing failed. Failed to execute (UploadServiceDefinition). Please consult the GP Results Window for enhanced error description or contact your administrator for the server logs." The only error it gives in the GP log is
ERROR 999999: Error executing function. Failed to execute (UploadServiceDefinition).
Not very helpful.
I am using ArcMap 10.3.1 and the National Park Service Organizational account that was working yesterday morning.