When cakes are cold when fondant is applied you can smooth it more easily with slight pressure; on a room temperature cake, that same slight pressure can cause bulging as you smooth the fondant. Your mileage may vary depending on the type/brand of fondant you are using.
Since ganache is firmer than buttercream, it could be that the top edge is “sharp” enough to cause the fondant to tear as you smooth it; I’ve had this happen on square cakes especially (and I’m crumb coating with buttercream). Sometimes it’s because I’ve rolled the fondant too thin, and am a little too assertive when smoothing it. If you soften the edge, it helps a bit - just run your impeccably clean (or gloved) finger at that edge and see if that helps.