Archive services are free and independently run, and they are sometimes down.
What to try
Wait and retry. Outages are usually short.
Check the status page. It checks the sources on demand and reports what it finds.
Reduce the load. A smaller result limit and a narrower date range make a search more likely to complete when a service is struggling.
Partial results
If some requests succeeded, Subdex shows what arrived and marks the set partial, listing what failed. Partial data is usually more useful than none, provided it is labelled — which it is, on every figure derived from it.
What still works
Saved research, exports of loaded data and every informational page work without a network. Only new searches need one.