I can't add any reviewers to my Pull Request.

When I click the suggested user I get "An unexpected error occurred" in red text where the suggested reviewer was.

When I try to type a different user into the reviewer box and click on the user I get "An unexpected error occurred" in red text in the Reviewers text field.

This results in no reviewers. This has been this way for the last 2 hours or so. I was able to add reviewers to a different Pull request yesterday.