Trouble with upgrading Gangplank's Ult in "Reccomended Items" tab in shop.

I just played a game where I managed to rack up 500 silver serpents to upgrade my ult as Gangplank. But when I went to the shop to upgrade it, it wouldn't work. I couldn't get any of the 3 upgrades. I wasted a few frustrating minutes trying to figure out how to get it to work. Eventually I went to the "All Items" tab in the shop and then it finally worked. Why do I have to upgrade his ult in a different tab of the shop? It's annoying that I wasted 3 minutes of my game because a stupid shop bug.