The total event rate for various EventLogging schemas shows a marked drop occurred around September 8/9. See the following screenshots from Grafana for the last 60 days:
- MobileWebLanguageSwitcher (somewhat smaller drop, but still clearly visible).
- Edit: Less clear, but at least the initial drop seems related (the maximum hourly values for Sept 9, 10 and 11 are lower than for every day since Jul 30)
A fifth example is Schema:Popups, where the issue arose first. Here shown for a particular event category on one wiki (the overall event rate for this schema has been affected by software changes and new experiment launches in the above timespan, so Grafana is less useful here):
This is being discussed in T146620.
Interestingly, Firefox does not seem to be affected there, which leaves Chrome as the main suspect in case of that particular schema (because it excludes IE and other browsers that are not SendBeacon compatible):
However, various other schemas don't show such a pattern: