SSRS report folder security not working for all reports

hi i am working on SSRS report and all my reports are go live now with all the user permission but not sure why permission is not working sometimes for some of the users.

i had set a permission for one user called domainName/Testuser to the folder(SalesReports) but don't know why permission is not working for all the reports inside the same folder.

is there anything i am missing to configure , please let me know.
do i need to set role(system user, system administrator) for all the users to site setting. i never add any user into site setting.. i just added into folder setting then folder security

Please any one let me know what i am missing to configure.