Looking at today's cash shop update, I've noticed that there is a limit on how many packs of cubes you can buy from the upcoming Double Miracle Time sale. However, if you look at similar sales from previous years, there wasn't any of these imposed limitations..
None of these sales last year had any restrictions on how many cube packs were able to be bought. If you look at the cube sales from the years before as well, they are also similar in where you have no limits on how many cube packs you can buy.