The Merge Agent failed to obtain a new set of identity ranges for the Subscriber. When troubleshooting, restart the Merge Agent with a higher value for -HistoryVerboseLevel and check the output log files for other server-related errors. Resolve any server-related errors before restarting the synchronization, or reinitialize the subscription.
The merge process failed. This might have occurred because the identity range check constraint could not be dropped and re-created.
If the identity range check constraint could not be dropped and re-created, check the security permissions, and also check whether the DDL changes are allowed on the table.
If the merge process could not find the Subscriber's identity range allocation entry, reinitializing the subscriber might fix the problem. The merge process that applies the snapshot creates the entry for the identity range allocation in the table.