ActiveAdmin Filter Time Out

When I search a User by email, which defaults to "contains", and purposely put in something I know it won't find, it times out and I get the standard "Application Error" page, the status being 503. Logs:

heroku[router]: at=error code=H12 desc="Request timeout" method=GET path="/manage/users?utf8=%E2%9C%93&q%5Bemail_contains%5D=zamm&commit=Filter&order=id_desc" host=www.appname.com request_id=4041fb8b-c14d-45ca-bdba-280d78bac6f3 fwd="198.0.42.137" dyno=web.2 connect=1ms service=30001ms status=503 bytes=0

If I search by last_name with a name I know doesn't exist, it does what it's supposed to, renders a "No User's Found" message.

Any idea why it would time out searching by email but not other attributes?

Using standard ActiveAdmin filters, ie

filter :first_name
filter :last_name
filter :email
filter :role, as: :select, collection: User::ROLES