Can't add items to Item sets

I've downloaded the recent update for my game to make a new item set for Kayle and everything was going fine and dandy; signed in as normal, clicked onto my profile button as normal and eventually made my way onto the item set tab and began setting up the item set page for Kayle. After naming it something and choosing the first item I was gonna add, I tried to drag it over to the box but it wouldn't add the item to it. I thought this was strange at first and I thought I did it too quickly like I normally do so I did it a lot slower a second time and it didn't work. I did it a third and fourth time even slower than each other but I couldn't add the item to the block. Same thing when I tried to add other random items to the item set; nothing would be added when I'd drag it over from the search menu to the item set menu. This also happened to other characters I tried to add items to.

I've tried reloading the entire game; stop game, start launcher and try again, but that didn't work and I even tried restarting my computer which also didn't work either. I'm on the most recent update for Mac Book and I'm on the most recent update of League- nothing happened to the update whilst I was downloading it. Help ;-;