It's the redirector that is flaky. The redirector normally redirects you to a mirror that is up to date.
https://www.trinitydesktop.org/mirrorstatus.php
As a workaround you can use one of the mirrors listed here but long-term you're better off switching back to the redirector once it is working consistently again.
(The status page says all the mirrors are out of date. I would not worry about that. Mirrors are updating all the time with test builds. The released versions are up to date.)
--Mike