This started happening around Dec 1.

These redirects show that it's related to some kind of deprecation.
https://build.chromium.org/p/chromium.webrtc -> https://ci.chromium.org/p/chromium/g/chromium.webrtc/console
https://build.chromium.org/p/chromium.webrtc/buildslaves -> https://build.chromium.org/deprecated/chromium.webrtc/buildslaves

Regarding the "Not Found" texts, the frame that became broken is this page:
https://build.chromium.org/p/client.webrtc/horizontal_one_box_per_builder (Still works)
https://build.chromium.org/p/chromium.webrtc/horizontal_one_box_per_builder (Not Found)

Oh, at least https://build.chromium.org/p/client.webrtc/horizontal_one_box_per_builder used to work, now it's just blank

https://chrome-internal-review.googlesource.com/c/chrome-golo/chrome-golo/+/520859

The following revision refers to this bug:
  https://chrome-internal.googlesource.com/chrome-golo/chrome-golo/+/e52e8f213e94313b0f549d4b4e5739cab157744a

commit e52e8f213e94313b0f549d4b4e5739cab157744a
Author: Erik Staab <estaab@google.com>
Date: Tue Dec 05 00:29:55 2017

https://ci.chromium.org/p/chromium/g/chromium.webrtc.fyi/console now shows status and the correct CLs (thanks Nodir for pointing out the repo was wrong)

and https://build.chromium.org/p/client.webrtc/waterfall now loads the status lines.

Let us know if anything else looks off.

Great, thanks!