Open-E NAS-XSR not responding/but still alive

We have 2 Open-E NAS-XSR ENTERPRISE Systems.

One of them is not responding for some period of time (few minutes) from time to time, but comes back to life after that. It seems to occur during file operations (copy, move) of larger files (5GB and up).

Can you help us?

Are there any errors on the left side of the screen with a red exclamation mark?
Could be several things RAID controller bottle necking, memory or NIC's. Is this with NFS or SMB? Can you provide more details or the log file?