Yeah this is the same thing that's happens every once in a while when a few deployments are triggered close together. From my understanding, there's not too much we can do about it at the moment with our gh-pages setup. I have a task in #1525 about porting the site to Netlify which @bebraw has said is much more flexible and could resolve the issue. I'll note this over there as well mentioning that Netlify may be a fix as this has come up somewhat regularly.

As with the other times, it seems the CSS file 404s for about an hour at most, usually less, and then the start returning again. Unfortunately, there's not really a "golden time" for merges/deploys as we have users from all over the world but hopefully we can start addressing some of these infrastructure things this soon, as we're much of the way through our content issues.

TLDR; See #1525