ArcGIS Collector sync error

[MollyMoore]

I am helping a field staff colleague troubleshoot a problem with syncing in Collector.  She is running Collector on an Android device (Samsung S5).  She has tried to sync while connected to WiFi and LTE (with data syncing enabled) without success.  I, and several other staff members, are able to sync from our mobile devices without issues.  I have attached a screenshot of the error message she keeps getting.  There are a few clues in it, but I'm not sure exactly what the issue is.  I would appreciate any suggestions about why this might be happening.

[Anonymous User]

Molly,

What version of Collector is the customer using? The latest for Android is 10.4.2

Are you trying to sync data that was published directly to ArcGIS Online or did you publish data to ArcGIS Server?

This looks like it may not be able to find the replica it wants to sync with. Were there any changes made to the map or the data while this map was downloaded to the device?

[MollyMoore]

I am waiting on a response from her about the version of Collector she is using - however, I am assuming it is 10.4.2 because she just downloaded the app about 2 weeks ago. 

The data are published to ArcGIS Server and consumed via a published feature service that is set up in ArcGIS Online. 

There were no changes that were made to the map or database while the offline map was downloaded to the device, so I am a bit baffled as to why it may be having trouble finding the replica. 

[Anonymous User]

What version of ArcGIS Server are you using? Is the user making edits to features in the map that are different from the features that other users can successfully edit and sync?