This has happened to me on my last 2 or 3 cakes. Here's my process: I crumb coat and put in fridge for an hour or so. Get my fondant ready. Pull out the cake and lightly coat with water so fondant will adhere to buttercream. I cover and smooth it. It looks great. Then I let it sit for a little while and I get big air pockets trapped between the cake and fondant. How do I avoid this? Any help would be appreciated.
The air pockets could be caused by covering the cake with fondant while it's cold. As it comes back to room temperature, air pockets may form.
It could also be caused by the fondant not sticking well enough to the crumb coat.
I've had this problem on my cakes too.
How smooth is your buttercream? I get it sometimes too but I find the smoother my buttercream, it seems like the less air pockets can form. If there are any gaps or unevenness, it seems like the fondant may not adhere (like someone else said) properly and you can get air pockets.
Thanks for the tips. I will try to get my buttercream super smooth. And perhaps skip the refrigeration phase