Unexpected Ledger State Replay in the Conway era
An issue was identified shortly before the Chang hard fork: it was found that ledger state snapshots would break ledger replay in the Conway era under mainnet conditions. The ledger and consensus teams worked rapidly to resolve the issue with a hotfix released within 24 hours of the hard fork. In order to avoid pauses in node availability, it was recommended that users should not restart their node process until they had upgraded their node to the hotfix - this included any node type: relays, block producers, DB-Sync nodes, etc.
The issue is documented here. The cause was a slight inconsistency between the ledger state snapshots that were written and those that could be read back; a side effect of the removal of pointer addresses in the Conway era. Nodes version 9.1.1 and later resolve this issue.