I cannot remember, but I want to say they said it was dangerous. I am taking a lot of their rankings with a grain of salt. This one, whatever it was, raised a red flag for me. I was planning on getting it because it is plain and easy to clean. The other ones look horrible to deal with.
My version with the recalled belt-strap is older and IKEA replaced it for free. But, as I wrote earlier, I personally never had the buckle come undone, but I do know that was the reason for the recall. Outside of that, I cannot imagine what could possibly be unsafe about it -- IKEA would have to recall the whole chair if it was unsafe and it's been around for many years. There's nothing unusual about it, the legs spread out for a nice wide base.
Anyway, I still highly recommend it for moms that don't want to fool around with elaborate high chairs with lots of features and parts and nooks and crannies and multiple trays with compartments, etc..