Not sure what can be done for this, but I was browsing the Arena using Tapatalk on my phone and I couldn't find The Slaughterhouse and WYP, along with the other restricted forums.
What's really weird is that I was able to see them there earlier in the day, but when I checked back a few hours later they were gone. O.o I'm on a desktop now and can see and enter the forums just fine so I guess it's an issue with the app?
Again not sure if there's anything that can really be done on the Arena's end, but I just wanted to let you all know.