Here's my take.  1.  the board is too thin.  2.  Did you level the cake then flip it onto the board?  Sometimes the upper edge has a shrinking problem and is slightly smaller in size than the other end of the cake.  So you fill it in with icing to compensate, right, well it looks like the filling in solution didn't work.  To prevent any movement the top and the bottom has to be the same size and it has to be on a very strong thick board.

Ok then, it sounds like "settling" over night.  One trick is to press down quite severely on the top of the unfrosted cake after it's been filled to squish out any air pockets left over in the filled area.  Some ladies place a tile or book on top of saran wrap on the cake and leave it over night that way in the fridge before icing.  Something moved.  If not the board and I know you're adamant about that part then it was the cake settling.  Another question.  Was your cake room temp or frozen during the icing process.  Frozen cakes  relax quite a bit during the thawing process.  Please don't get offended by my freezing question (some bakers are touchy about this subject)...............I'm seriously trying to help you out and am pulling out all the old tricks I've learned over the years in the "Don't Ever Do Again" part of my brain.

ANot offended at all! ;-). I appreciate the help.

Cakes were left to settle 18 hours with a Cake pan on top before iced. I don't freeze or fridge my cakes. After I unwrapped the cakes from settling for 18 hours I let come to room temp for 3 hours then added crumb coat. I left crumb coat on cakes for about 5 hours before icing them in the final coat.

Thx for the help!

So confused.  If you don't freeze or refrigerate your cakes then why do you need to have them come to room temp for 5 hrs.  They're already at room temp, correct?  You're doing everything right, but there's something you're missing, we're missing - new cake recipe, left out some ingredients, forgot an ingredient or accidenatlly left out an ingredient.  If it's a homemade (from scratch) recipe then I have no clue - if it's a box mix then possibly the manufacturer changed something in the box (like Duncan Hines did last Winter) and all our cakes fell.

Could it be the shortening or your ingredients in general? If you are doing the exact same thing for years and then this happens, it could be the ingredients.  Maybe the coffee creamer has added something or changed something, or maybe the shortening manufacture has changed their formula? I love how smooth your icing is and you once told me you used Sharon Zambito's recipe.  Is that the same recipe you're using? I don't have any idea why this is happening.  Just a thought.  

A

When I let then settle overnight they are in food safe plastic bags. When removed from plastic bags there is condensation on the cake. Condensation is a huge problem if not dried. Reference Sharon zambitos icing method. I like the crumb coat to be firm before I ice.

Thanks.

A

Thanks. ;-)

Yes still using Sharon's recipes. Not sure if any of the manufactures changed anything or not?? Maybe so. But the shortening was used in past cakes with no issues???

Someone mentioned humidity might have been the culprit?? Maybe so...

I really appreciate the help.

I am wondering if it is the creamer? I tried the "getting water and creamer hot" thing, and found it much too crusty. I just use cold cream in mine, and it gets super smooth. 

ASometimes that just happens with a crusting butter cream. Could be movement or settling. Or dry air or just nothing. Try more shortening in the icing. To make it not so crusty.

AJust read the cakes were stacked. It was prob pressure from the upper cake as the dowels settled a bit. It doesn't take much to make the crust shift and crack. This happens to me too sometimes. ESP if. I dowel a smudge too low.