Same gravatar is displayed for different users in the stackexchange.com [filters page](https://stackexchange.com/filters/118502), 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]( https://www.gravatar.com/avatar/66c66c4d97a7bc3859a85253f003e1fb?s=18&d=identicon&r=PG&s=30) 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.

> [![Same gravatar][1]][1]


  [1]: https://i.sstatic.net/TvLk6.png