Collector on iOS 10.3.8, feature service on ArcGIS Server 10.3
When I download a map in Collector, I can visibly check that a replica gas been created on the server. However, when I try to sync, I get "Replica with this GUID does not exist on the server" as if the replica has been unregistered. It is strange that the error message does not show the specific GUID number; it just says "this GUID". When I remove the downloaded map within Collector, it does not unregistered the replica.
In addition, I cannot reproduce the error consistently. I use the same web map that pulls the same feature service, make no changes and download a new map in Collector and the sync works fine! And it also unregisters the replica when I remove the map.
Any idea what's happening here?