Unimus forum

Hi,
We have 52 devices.
In those, we have 4 ArubaOS switchJL255A 2930F-24G-PoE+-4SFP+.
For one we have this message in logs when backup : "'Timed out waiting for any known data from device (timeout: 30000 ms)'"
Discovery is OK
What can we do to solve this problem please ?
Regards,
Philippe