I just did some testing and have the following finding:
I have enabled password protection for the folder wp-admin previously. After I disabled the password protection, the problem disappeared. But when I enable it again, the problem comes back.
Seems it is related to that wp-admin folder. But why MDTF need to access wp-admin? But it seems not really accessing wp-admin because the page could be viewed if I click cancel in the sign-up box….
