I'd like to ask if anybody knows why all bridges suddenly go offline at random times? It can be viewed via the Tor metrics chart which shows how number of active bridges often hits zero and then comes back.
Tor Metrics uses a backend server to collect the data from different sources. From time to time this server becomes unreachable, crashes etc. So it doesn't collect data for a short amount of time. You can see the result of it in the diagramm above. Usually it is nothing to worry about. Also the bridges are online the whole time. So if you are a bridge user, you can use it like any other day.