A small part of Stream's customers was impacted by an issue that caused notification feeds to be temporarily unavailable.
Earlier today at 15:30 GMT a maintenance database migration was initiated; unfortunately the procedure did not clear the cached state of feeds correctly. This lead to reads not showing activities from before that time. At 16:00 UTC we remediated by flushing the stale cache which immediately fixed the problem. The issue did not affect any write operations such as adding/removing activities or following/unfollowing feeds. After some investigation we could find and amended the incorrect part of the maintenance operation. Apologies for the trouble and for bringing this up during the week-end.