Mattermost change history: Collapse threads are not functional in part of Cloud workspaces

Collapsed threads were not functional in some Mattermost Cloud Workspaces during a major-impact incident that started at 2022-01-26 09:05 UTC and was resolved at 2022-01-26 16:04 UTC, lasting 6 h 59 min. Mattermost reported identifying the root cause and working to mitigate affected workspaces, but did not specify the cause or fix.