All clients that relied on the mainnet Hiro API. This includes the Explorer, Stacks desktop and web wallets, the stacks CLI, and others. Requests on all endpoints to the mainnet API were unable to be served.
After scouring our infrastructure, events, metrics, and third party services, we believe brief GCP network instability is what caused this short outage based on general issues on their status page around the affected time: https://status.cloud.google.com/incidents/7BkNzwMsik35A2V5j6vM#FxgErUaBEZS6pEeX6yiz
https://status.cloud.google.com/incidents/qv2VvxMoAzY8xgH4bsLQ