on friday 15th bromine started having load issues, investigation showed a big (700k) js asset not being cached (all varnish pass) being the culprit and driving bromine's load up and making 15.wikipedia.org slow to load
further investigation revealed a problem when apache was serving gzip responses without content-length to varnish, making them uncacheable.
the issue was fixed for bromine by @ori with https://gerrit.wikimedia.org/r/#/c/264315/1/modules/annualreport/files/15.wikipedia.org though more apaches are potentially affected