Same gravatar is displayed for different users in the stackexchange.com filters page, under the Top Network Askers in the right side bar.
The red circled image's source (<img src=) are from
https://www.gravatar.com/avatar/?s=18&d=identicon&r=PG&s=30
^
Seems the gravatar id is missing here in the image source.
For an example from the list, the user Mad Scientist's gravatar id should be
https://www.gravatar.com/avatar/66c66c4d97a7bc3859a85253f003e1fb?s=18&d=identicon&r=PG&s=30
but it is mapped with
https://www.gravatar.com/avatar/?s=18&d=identicon&r=PG&s=30
which caused the display issue.
