I got this error when trying to add or delete a point in Field Maps. The way I was able to resolve it (at least for the time being) was to go to the Settings of the layer from within ArcGIS Online. Then beside "Manage Spatial Indexes", I clicked the button to "Rebuild Indexes." When I tried adding or deleting a point in the Field Maps app after this, it worked.
When I created a polygon using Field Maps, I needed to make a revision which entailed adding a new point and moving a few other points from their original location. Later when I checked my map, I got the "service error code for 1000" on the Field Maps app. How I resolved my problem was going to Settings in the feature layer and deselecting the polygon layer under "Optimize layers". I believe my problem started when created my feature layer and I selected the optimize layer option before I shared the map with my group. So once I stopped using "Optimized layers", my map was able to sync.
