1. Agent has no write access in the system.
Check system permissions and make sure that on this computer the agent has read-write access to the file and all parenting folders.
2. Time difference between agents is more than 600 seconds.
Check UTC time on all agents and compare results - it has to be the same:
OS X/Linux in Terminal: date -u
Windows in Command Prompt: for /f %x in ('wmic path win32_utctime get /format:list ^| findstr "="') do set %x
Run the command with minimal time lag to get more accurate results for comparing.
3. Files are currently being in use.
Close all apps that might be keeping the file and preventing other apps from accessing it.
4. This is a Read-Only share
If a non-synced agent has Read-Only syncing access to the folder, syncing will stop if a file gets updated on it. Since this is a read-only share, the updated file will not be uploaded. To eliminate this problem, make sure that in the Profile assigned to this agent's group the "Overwrite any changed files" option is set to YES.
5. Agents are not connected to each other.
Even though they are all connected to Management Console, it does not guarantee direct connection between the agents themselves. Check network settings to allow traffic on these ports.
If neither of the tips helps, please collect logs from agents and Management Console, and send them to support.