Stability of HTTPS for w3c-test.org

https://w3c-test.org has been slow or down multiple times for me over the
last month or two that I've tried to use it. A few minutes ago, it was
failing to connect at all on multiple computers and browsers then suddenly
started working.

Is the stability on HTTPS a known issue? Are there plans to address it?
With tests being written using features that require HTTPS, it's important
that https://w3c-test.org be reliable.

David