Sorry I need help! My cakes are shifting when I stack them.  My leveling wasnt bad and I used a level and it said my cakes were level. The only thing I can think of is the buttercream frosting is causing them to slide. Its like the back bulges out. I frosted and stacked them at room temp both the cake and frosting. 4 layer 10 inch cake is what I made. I had to take my hands and shift and wiggle them back straight.  Maybe the cake settles??...I have no idea why this keeps happening but its frustrating. It happened right when I stacked and frosted them so it didnt really have any time to settle.  

How much & what kind of fill are you using?  Did you make a dam then fill no higher than  it?    Did you use a cake circle between —stack 2 layers then put in  support straws before adding the other 2 filled layers w/a cake circle under it?   10” tiers ( 2 layers w/filling between) are to heavy to Just be stacked w/o a support system.  

Also what exactly is the icing recipe you are using? —-so we can tell if that could be parrot all of the problem

Yes I use support and cake circles and there is no filling....just all buttercream but I still make a dam.   My recipe is 5 1/2 cups of powdered sugar...1 1/2 cups of butter...5-6 tbsp of milk amd 1 tbls of vanilla flavor. I add more powdered sugar or less depending on the consistency. I think I need to make my frosting stiffer for the middle in between each layer. 

I can only think that perhaps the buttercream is a little too soft or that there is too much of it between the layers.  It would probably help if you chilled the cake layers before frosting.  Cold cakes are much easier to handle.

I heard chilling the cakes amd then frosting makes air bubbles.  I have heard so many diffferent things my head is spining

Each person does what works for them.  I am giving you my personal experiences and preferences.

By the way, I keep my cake refrigerated all the time.  Whether I am in the process of decorating or after the cake is finished, if I am not working on it, back into the fridge it goes.  My preference.

I have worked in many bakeries and etc beside my own stuff I did from home -- any iced cake will fart -- that's what I call cake blow outs -- the only real control I know of is to put an opening, a small hole in each layer through the icing into the cake and leave it open -- try to conceal the holes behind a flower or whatever -- this gives the trapped air somewhere to escape --

but as far as leveling and layers shifting and being able to slide the layers back together after icing the cakes -- idk -- I fill my cakes a tid tad in from the edge so there's a little play there -- I use the same icing for the filling as I do for the sides -- even for dam's even with cooked icing that are lighter --I

seems like a lot of butter -- I used two sticks of butter aka one cup to two pounds of powdered sugar which is 7.5 cups -- but there are no absolutes in any of this stuff--

are you mixing your icing for ten minutes or so?

I’m w/K8 & Sandra on this... there is no absolute... what area of the world are you in?  That has some effect.... have you tried other recipes for the icing??  The one I posted is being used by many with good results.  It is a bit on the soft side.   Since you say you are checking the level I’m just lost what to say.   What kind of level are you using?   ..... just grabbing Straws trying to figure something out for you ....