Hello Esakki Selvaraj,
Thank you for posting in Q&A forum.
You can check this Administrator's permission on this group via right clicking this group, then click Security tab\click Advanced button\Effective Access:
User/Group: type or select Administrator
click View effective access.
If there is Read members and Write members permissions.
And check if you can see any Deny entry (all entries are Allow below) under Type as below. If there is any deny entry, then check if it is related to this administrator (deny read members).
I hope the information above is helpful.
If you have any questions or concerns, please feel free to let us know.
Best Regards,
Daisy Zhou
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