Thursday May 20, 2021


Service degradation in Slack

Issue summary:
On May 20, 2021 from 10:30 a.m. to 10:55 a.m. PDT, some customers experienced errors and degraded service while using Slack. While a subset of workspaces had trouble accessing Slack, some customers were not impacted at all.

We discovered that a code change had inadvertently affected some workspaces' caches. This change was intended to prevent the Slack client from retrieving data from a deprecated cache schema. However, a missing field in the new cache schema meant that references to the original schema caused fatal errors.

By 10:55 a.m. PDT, we'd reverted the change and ensured that the system was fully recovered for all affected customers. Some customers may have had to restart the desktop app, reload their browser tab, or sign back in to the mobile app to access Slack.

Note: We know our customers rely on Slack. If you'd like to receive a full Root Cause Analysis (RCA) report, please reach out to to request one.

7:12 PM PST

We've released a fix for this issue, and Slack is up and running once again. If you are still experiencing any trouble, please fully quit your Slack app or browser using Command + Q (Mac) or Ctrl + Q (Windows/Linux), and then reopen it.

Thank you very much for bearing with us on this, and if you're still encountering any trouble after a restart, let us know at

Note: We've verified the actual duration of this issue to be between 10:30 a.m. PDT and 10:55 a.m. PDT. The timestamps of these updates have been edited to reflect this. We'll be back with a summary of this issue shortly.

10:55 AM PST

Some users may be experiencing issues loading Slack. We're actively digging into this issue and will report back as soon as we have an update to share. We're sorry for the inconvenience in the meantime.

10:30 AM PST

Services affected




Link Previews






Workspace/Org Administration