Not actual "Author" filter content in pull requests

[Arkadiusz Niewiadomski]

Hi,
We've found an interesting issue. When coming to a company repo, no matter which one, and selecting the pull requests from left-side menu I see filters in the navbar next to search input.
After clicking the Author filter a dropdown menu expands with list of users but the values are not actual - there are plenty of users missing even though on the list of pull-requests I see them in default (no filter) view.

Does anyone know maybe what needs to be done to fix it (at list make more actual)?

Many thanks in advance

Arek