Maybe the featureclass was modified after the mobilecache was create for the field computers, thus causing a checksum problem for syncing.
I would suggest creating a new featureclass with global IDs and then creating a project and loading it into each of your field computers.
Then try syncing again.
If that works then I do believe that the featureclass was modified.
Otherwise you may need to provide more information about he featureclass and how you loaded the the project onto each computer.