Major store bug - completely inoperable

Clicking on any tab of the store, including the Featured tab itself, will cause the store session on my Window 8.1 laptop to immediately expire. It will show the apology page and then reset the page to the Featured tab.

There is a (slightly unreliable) workaround - clicking on a tab, then immediately clicking on another tab, then double clicking the tab you want to go to, will cause the store's automatic reset to focus on that tab instead. However, it turns out that these pages don't allow you to make purchases and neither remove IP from your account nor give you the champion or skin you have purchased.

There are no steps to repro - either the store is bugged on your machine or it is not.

Disconnecting, relogging, and restarting do not solve the problem.