I love the taste and convenience of using Sam’s club buttercream.  I have tried several times now to use it with cream cheese for my carrot and red velvet cake.  It never comes out right.  It taste amazing when I finish blending it’s all nice and smooth, just beautiful.  About 15 mins later when I am ready to fill and frost the cake it has begun to separate.  There are small chunks of the cream cheese that are sticking out and clogging the pastry bag.  It isn't a smooth finish on the cake 

Is there a way to do it correctly and avoid this or is scratch cream cheese buttercream the only way to go?

Thanks for all advise