[CLIENT] Can't purchase Mystery Icon from store

[DESCRIPTION] I can't purchase the "Mystery Icon" item from the store; it says that my available pool of items is 0, despite the fact I have numerous unowned icons.

[REPRODUCING THE ISSUE] This past winter I purchased the maximum number of "Mystery Icons" each day until all icons except one were unlocked. For some reason it wouldn't allow me to unlock the last icon via purchase of a "Mystery Icon". Strangely, the error returned was "In order to unlock a Mystery Item your available items pool needs to be 1, and currently your available items pool is 0". As such I bought the last icon directly, thinking it wasn't a big deal.

Now the "Mystery Icon" item is available in store again, and I have numerous unowned icons (I hadn't purchased any icons since December 2016); the store still gives me the same error message as before despite the fact my available items pool is definitely greater then 0.

I have posted a link to a screenshot of my issue. As you can see in the background I have many unowned icons.