There are some Ikea products that are difficult to assemble in a lasting way. They are the exception though, and they're always the cheapest things.

The smallest Lack coffee table (€10 or so) is assembled with double-ended screws from the legs into the tabletop. There's no way it can take any sideways stress, e.g. by someone leaning or standing on it. A child falling onto the table can break it.

The larger Lack coffee table has the same legs, but adds a thin shelf for additional structure. If the shelf is loaded with a few books, it bows after a while. (I have this table.)

There are similar problems with the €10 metal furniture.