Reporter Dropdown List shows unnecessary names.

[Alex Sim]

Is there any way to remove these kind of weird users from appearing in my reporter dropdown? 

[Petter Gonçalves]

Hello @Alex Sim

Thank you for reaching out.

The users you are displaying in your screenshot are related to the third-party apps you are currently using in your site and, unfortunately, it is not possible to restrict these users from being displayed in user picker system fields, except by the Assignee field (Which you can restrict using the Assignable user permission).

That being said, we understand how the displaying of these users can be annoying, so we created the following feature request to allow the restriction of these users for system fields (Including the reporter field):

Limit User Picker to members of certain groups/roles in System Fields 

Feel free to vote and watch the suggestion to increase its priority and also receive notifications about any updates.

Let us know if you have any questions.