Did you talk with Suzuka at night? I remember her talking about howlings at night, which then triggers the poster in the notice boards.
I can't seem to get any type of trigger for them to mention howling. I tried talking to them at 19, 20, 21, 22, and 23. I tried to see if maybe it wouked at late night, and nope.
I even tried to see if maybe it would work doing a threesome at night at both the tent, and Kagami's place at I got nothing.
I'm basically still stuck at step 1 for Kagami x Suzuki's EX scenario. I've already finished Yui x Mizuki, Rio x Shizuku, Miyuki x Kanae, and Akari x Kikari.