unable to remove group members using Remove Group Members.

Hi,

We have use case to provide a user task to create a group and add members to that. we are unable to remove the existing group members. but can able to remove the newly added group members. for this we are using Remove Group Members and Add Group Members services in Process model.

Can you please provide some pointers to check this issue. Process model activity didn't throw any error when we are removing the existing users but it doesn't happening.

Thanks in Advance.