I have actually experienced this same downtime error ones since bitcointalk banned mixers and this forum started getting traffic, although the day I experienced this, it didn't last long, I think I left the forum and returned back again to check in about two minutes or three, and the error was already cleared.
I would actually say that this is completely normal as long as we are on a forum they is growing, if the server is not strong enough, there is high chance that when ever the forum gets high traffic, or ddos attack, there will always be such a down time where such error will be displayed to users trying to access the forum.
Personally, I would say that, this is not something to panic about, atleast not for now, except the down time becomes more constant and prolonged unnecessarily, then, and only then should it become a thing to be concerned about.