Bug filter by Cognito listUsers or on the cognito backend console

Hi,

I have an cognito record, its preferred_name is:shan, but when I search this with "shan" on the cognito backend by preferred_name, there is no result, I am suer I have this record, then when I use "sha" to search, it can list in the results.

could you please advise on why this happens and how to resolve it?