This issue has been resolved. All sandboxes, including those created during the incident, are now correctly returned in list results.

The issue was caused by a disruption in the internal service responsible for indexing sandbox data. The underlying cause has been addressed, and we have taken steps to prevent a recurrence.

We apologize for any inconvenience this may have caused.

Since 11:35 UTC, sandboxes created after this time are not being returned by the sandbox list endpoint (GET /sandbox). Sandbox creation and direct lookups are unaffected.
We have identified the cause and are working on a fix. We will provide another update shortly.