Between May 2nd and 7th, Polkadot parachain block times experienced a period of degradation. Andrei Sandu (Parity) has published a post-mortem. The cause of the issue related to disputes originating from a single validator suffering from disk failures. In each new session the faulty validator was added to the list of disabled validators after losing a dispute. Due to a bug, the list of disabled validators clears when a validator restarts. Thus, any restarted validator would join disputes raised by the faulty validator, triggering a dispute storm. The issues have been patched in the stable2503-4 release.