This is probably the same as https://github.com/acreloaded/acr/issues/193
The master-server sometimes has issues, but it is currently working. Just now, I saw one server on it.
Unfortunately, there are almost no servers and players because ACR started with few servers and players and failed to grow. Even worse is that ACR has been inactive recently, but a new release will be made around the start of January. This is almost a year after the previous release, in contrast to the frequent releases in the past.