A small fraction of our userbase experienced an unexpected "paused by system" of their monitors on April 18, 8:00 AM UTC. As of April 19 11:30am UTC, all such erroneously paused monitors have been resumed and are functioning as expected.
We suspect that this happened because of the monitoring system misrepresenting one of our maintenance activities as unavailability of the underlying data. We are working towards applying additional guardrails to prevent this from happening in future. We understand that this was a disruptive event and we take this very seriously. The activity logs for your monitors should show the relevant "pause" events, and will soon show the "resume" system event as well to reflect the incident window.