MirrorSync Server Error

I client of mine is getting this error every time they try to sync.

Quote

Apr 24, 2019 10:35:41 AM com.prosc.mirror.config.server.SyncServer$3 call
SEVERE: Sync between 192.168.1.42 / MtLebanon (FileMaker Server) and BJ2015#( username 'beta', running Go_iPad 17.0.5.500 on 192.168.1.155, ping time: 436 ms, machine name: 'MLA Dan's iPad' )
Last sync failed: com.prosc.sync.AbortException: Could not get sync state for syncId 6416

Any thoughts on how to correct this would be appreciated.