I can't repro, I think it has to do with a bad state during a running build.

I could reproduce in
https://ci.chromium.org/p/chromium/builders/luci.chromium.try/win7_chromium_rel_ng/151936

screenshot of bottom is
https://screenshot.googleplex.com/94ypMbWVPAU

timelineDelta json is
https://paste.googleplex.com/5434697848979456

I also got following warning from viz-custom.min.js in console when I saw broken timeline
"Something is wrong with the Timeline scale. Limited drawing of grid lines to 1000 lines."

It probably barfed here: https://screenshot.googleplex.com/sGbhX4hULBN

Sorry for the dumb question but - how are you running these builds against the timeline code? During development I used:

make up-dev-default

which appears to only provide an instance over some canned data. I didn't know there was a good way to get the timeline running over the production data.

Per comment #3: I saw that a couple of times during early development - IIRC I even surprisingly had this happen per some css changes that apparently effected the scale in ways that the timeline code didn't like. Thanks for the report.

Per comment #4: Excellent, thanks.

> Sorry for the dumb question but - how are you running these builds against the timeline code? During development I used:

In the time I reported this issue, prod showed timeline.
But it is disabled now again?

I didn't know prod was showing the timeline. If this is the case I believe Ryan took it back down so that he could do some refactoring on the build page to accommodate the buildbot deprecation before rolling this out.