same issue. I have submitted a ticket, I will update if i get a solution.

Hi

Did you get a solution for this issue, i have got the same problem

Thanks in advance

OneFS statistics is only looking up or caching a limited number of user names per sampling interval,

but the numerical UserID field should have accurate information.

hth

-- Peter

Solution :

Isilon stores 1024 user name records for each 15-second window. An UNKNOWN user name is not included in the 1024 records for the window in which the command was issued.

from this doc :

https://support.emc.com/docu78704_Isilon-OneFS-Cluster-Performance-Metrics-Tips-and-Tricks.pdf?language=en_US