The masterlist was offline for about 30 minutes, starting around 23:00 GMT. This was caused by an unsmooth transition from SQLite to MySQL. During this time period, the masterlist would return no or malformed data, which would, at times, crash the browser due to unexpected results.
This issue appears to have been resolved, and servers should disappear at random less often, if at all. If this is still an ongoing issue, please report it immediately.