Did you figure out what was causing this for you?
I have been having the same disappearing edits problem recently. I noticed however that since the update last week that the option to Create Local Copy for Editing is no longer available when I pull certain feature services into ArcMap. Anyone else seeing these issues?
Update: "Create Local..." is fine, I had both a map service and feature service going and was grabbing the wrong one...
As for the syncing, I was working on and off with ESRI technical support and in my case it seems that there were attribute fields set to not allow null values in the original data causing kind of a silent fail when not populated.
Turns out the null values was my issue as well.