Ive used ganash, ALOT. I love it, it goes perfect with a chocolate cake and i find it a better medium to work with than buttercream (i can never get right consistency of that lol )
Anywho, i made a cake this week, The same ganash , The same cake recipe, Just two layers, and i covered with my usual fondant. It was a 9''x5'' rectangular cake. i filled the cake with the usual amount ( i like to measure it out ) and then covered the cake with the rest, i use pretty much the same amount everytime and have never had an issue.
Yet with this cake, it buckeld, and you could see under the fondant, the bulges, Not from the middle/filling , But near the very bottom, almost as if the ganash had completely slid down to the bottom. Also i didnt have any decorating on the cake besides the fondant, which wasnt thick, so there was no extra weight on the cake at all.
I cant understand why this happened at all, ive made dozens of cakes this way and never ever had a problem. Oh btw, after applying the ganash, i let it sit for an hour to settle, then covered it with renshaw regalice
Not sure where you are from, but I too had the same issue about 4 weeks ago. About the time humidity and heat took over Florida. I was using buttercream, not ganache. But it looked like the buttercream had slid to the bottom. Never happened before. I've been turning my AC down very low ever since.